In 1997, a case of flock workers' lung occurred at Claremont Flock Corporation. The National Institute for Occupational Safety and Health (NIOSH) conducted a health hazard evaluation (HHE) in 1998 at several of Claremont Flock's plants and found that cleaning with compressed air and bagging flock were associated with worker-reported symptoms. The HHE report provided environmental and medical recommendations to the company to prevent flock-related disease in their plants. In March 2004, based on a case report consistent with flock workers' lung at Claremont Flock's only remaining plant, the Massachusetts Department of Public Health Occupational Health Surveillance Program requested technical assistance to determine if there had been improvement in the environmental conditions and to update the health status of the workforce. NIOSH conducted environmental and medical surveys at this plant in January 2005 to characterize exposures and symptoms of flock-exposed workers and internal comparison groups. The environmental survey consisted of personal time-integrated gravimetric sampling for respirable dust concentration and sampling with aerosol photometers to obtain real-time continuous relative levels of dust (approximately respirable) during some plant activities. Videotaping was done to record events that might be associated with any observed peaks in real-time readings. We invited all 80 employees to take part in the medical survey. Trained NIOSH interviewers administered computer-based questionnaires that focused on respiratory and systemic symptoms, physician diagnosis of respiratory illnesses, smoking, work history, respirator use, and whether fit-testing had been conducted. Time-integrated respirable dust sampling results showed that the bagger/cutters and the dryer operators had the highest geometric mean 8-hour time-weighted exposures of 0.13 and 0.80 mg/m3, respectively. For most groups of workers, the exposures were found to be largely unchanged since our previous investigation in 1998, but for these 2 groups of workers the exposures were found to have increased. This happened despite the engineering control changes made in the plant since 1998. Real-time personal sampling results indicated that cleaning operations, such as blowing with compressed air, sweeping, and shovelling of flock, were associated with increases in dust levels around the workers. Manipulation of bags of flock both inside and outside of designated "respirator-required" zones at bagging stations was also associated with elevated levels of dust. A total of 74 employees (participation rate = 92.5%) participated in the medical survey. The majority of employees were male (92%), white (58%), and non-smokers (76%). The mean tenure of Claremont Flock workers was 8 years, and only 16% of workers had either changed jobs or started working at Claremont Flock within the last 6 months. A total of 22 participants (30%) reported cleaning with compressed air for at least one hour per week, and 23 participants (31%) reported working with cotton in the last 12 months. Except for bagging cotton, there was an increase in the percentage of employees who wear respirators during their activities, when we compared the 2005 and 1998 surveys. The percentage of fit-tested workers also increased in the 2005 survey compared to the 1998 survey. The most frequently reported symptoms were wheeze apart from colds, throat irritation, and sinus problems. The prevalences of throat irritation, usual and chronic cough, shortness of breath while walking up a slight hill, and wheeze apart from colds were lower among never smokers compared to current or former smokers. When we took into account only symptoms with onset after employment at Claremont Flock, chronic phlegm and shortness of breath were the most frequently reported symptoms. "Wheeze apart from cold" and "pneumonia in the last year" were statistically significantly elevated when we compared symptom prevalences of participating workers to expected prevalences based on national data. In general, dryers and baggers/cutters, workers who cleaned for one hour or more per week using compressed air, and employees with high cumulative exposure to flock-associated dust (> 0.425 mgyear/m3) had higher prevalences of symptoms than other workers. In multivariate models, cleaning equipment with compressed air was significantly associated with throat irritation. High cumulative exposures were significantly associated with the development of sinus irritation. A comparison of 1998 symptom prevalences for a subgroup that participated in both the 1998 and 2005 surveys indicated that those who continued working had lower symptom prevalences than those who had left after 1998. This is a form of "healthy-worker effect", whereby health effects of a workplace exposure are underestimated by looking at current workers. We conclude that working with flock and cleaning with compressed air are associated with health effects at this plant. We recommend that the company prevent flock-associated dust exposures: by providing engineering controls and improving work practices for the bagging process including not only the filling of bags at the bagging stations but also the subsequent manipulation of the bags for weighing, sewing, and palletizing; by determining and controlling the source of elevated dust levels during production in the dryer rooms and repositioning the dryer room bagging station local exhaust ventilation hoods to the tops of the bags being filled with flock; by providing new cleaning methods that will eliminate the elevated dust levels associated with compressed-air blow-downs, sweeping, and shovelling of flock; by verifying effectiveness of controls with regular air sampling; and by expanding respiratory protection requirements, until the controls can be implemented, to all bagging and flock-cleaning processes, including manual unplugging of accumulators (enclosed baghouses), and to the entire production operation in the dryer rooms. In terms of medical recommendations, we suggest that the company continue to offer a smoking cessation program and to enforce the no-smoking policy already in place; include in the current respirator program a means of identifying workers with respiratory symptoms such as shortness of breath, wheezing, or phlegm production, and a means of detecting declines in lung function; and provide information about flock workers' lung to employees and health consultants responsible for the respirator program. We also recommend that employees wear respirators when required; handle bags of flock with care to prevent airborne flock; seek medical evaluation for respiratory symptoms, such as shortness of breath, wheezing, or phlegm production and inform health care providers of flock exposures; and inform management of respiratory symptoms and associated flock exposures. The Claremont Flock plant in Leominster, Massachusetts was first evaluated by NIOSH in 1998 as part of its initial investigation of the risk of occupational lung disease from exposure to flock-associated dust. In 2004, after learning that a worker at this plant had been recently identified as having medical findings consistent with flock workers' lung, the Massachusetts Department of Public Health Occupational Health Surveillance Program requested NIOSH technical assistance to determine if there had been improvement in environmental conditions at the plant and to obtain updated information on the health status of the workforce. NIOSH conducted a medical and environmental survey at this plant in January 2005. Despite engineering control changes implemented after 1998, respirable dust levels were found to be unchanged or increased. Upper respiratory symptoms were associated with cleaning equipment with compressed air, and with high cumulative exposure to flock-associated dust. To minimize the risk to workers, management should improve work practices and increase mandatory use of respirators by workers while it identifies and implements additional engineering controls.