On December 12, 2006, the National Institute for Occupational Safety and Health (NIOSH) received a confidential Health Hazard Evaluation (HHE) request from workers at the Solae Company's plant in Memphis, Tennessee. The requesters described respiratory symptoms and diagnoses, including sinus congestion and asthma, which they attributed to the workplace. They noted exposure to soy materials, lime (calcium oxide (CaO)), microbial contaminants such as mold, and insects. NIOSH investigators conducted telephone interviews with workers, a union representative, treating physicians, and company management and safety officials. On March 6, 2007, NIOSH investigators visited the plant to observe the process, measure concentrations of airborne dust, collect bulk samples of soy materials, and interview workers about their symptoms and exposures. They later conducted an industrial hygiene survey (July 9-13 and July 30-August 3, 2007). NIOSH investigators collected personal and area air samples from different plant areas, sub-areas, and jobs during the survey. They collected: personal (breathing-zone) air samples for inhalable dust and inhalable soy antigen; personal (breathing-zone) and area air measurements for airborne dust of respirable and thoracic size fractions using a real-time sampler; and area air samples for inhalable dust, inhalable soy antigen, total dust, total endotoxin, selected metals, and particle size distributions. They also collected bulk samples of soy materials from different sub-areas of the plant. From July 23-August 2, 2007, NIOSH investigators also conducted a medical survey of current workers at the plant; it consisted of an interviewer-administered questionnaire; lung function testing, including spirometry, bronchodilator, and methacholine challenge testing; and skin and blood allergy testing. Inhalable dust exposures were highest for the autopack operator, unloading switch operator, and sanitation job categories. Some of the samples from these job categories, as well as from starch dumping, exceeded the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for total dust as particulate not otherwise regulated (PNOR) and the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit values (TLV®) for inhalable dust. The task of starch dumping, which produced the highest dust concentrations measured (21.7 mg/m3), was typically done by workers from several different job categories outside their normal shift work, using respiratory protection. Detectable soy antigen air concentrations were measured in all plant areas and sub-areas; the highest geometric mean inhalable soy antigen area concentration was in the flake processing room (308,000 ng/m3). Job categories with the highest geometric mean soy antigen concentration as measured by personal samples included the unloading switch operator (27,540 ng/m3), curd operator (25,960 ng/m3), and unloading lead (14,360 ng/m3). Currently, there are no occupational exposure standards or guidelines specifically for soybean dusts, though the more general PNOR standard does apply to soybean dusts. The highest endotoxin concentration, 217 EU/m3, was measured in the flake processing room; all other endotoxin concentrations were below 50 EU/m3. Calcium was detected in 5 of 67 total dust air samples; if the calcium in these samples was all present as lime (CaO), the highest corresponding lime concentration in air would have been approximately 0.52 mg/m3, a level well below the existing OSHA standard for lime dust. Of the 281 workers currently employed at the plant by the Solae Company, 147(52%) consented to participate in the medical survey and completed the questionnaire. Participation rates varied by worker classification, ranging from 66 of 94 (70%) production workers to 42 of 114 (37%) non-production workers. NIOSH staff conducted lung function testing for 140 of these workers, skin allergy testing for 132, and blood allergy testing for 135. Participating workers at the Solae plant in Memphis had higher than expected prevalences of physician-diagnosed asthma, sinusitis, and wheeze (a symptom of asthma) compared to the U.S. adult population. The prevalences of current and ever physician-diagnosed asthma for participating males were higher than expected based on a survey of the state of Tennessee, but these differences did not reach statistical significance. Among participants with adult-onset, physician-diagnosed asthma, most were diagnosed after hire at Solae. The incidence rate was five times greater after hire than before hire, consistent with a temporal relationship of occupational exposures preceding asthma diagnosis. Compared to non-production workers, production workers were more likely to report asthma-like symptoms that improve away from work. Work-related asthma-like symptoms were also associated with peak dust concentrations. Compared to workers exposed to lower peak concentrations, participants exposed to higher peak concentrations of dust were more likely to report work-related asthma-like symptoms. Additionally, workers who reported seeing or smelling mold in the workplace were more likely to report work-related sinusitis, nasal allergies, and rash compared to workers not reporting this exposure. Fourteen participants (10%) had airways obstruction on spirometry (six borderline and eight mild or worse severity). Eleven (8%) had spirometry results indicating a restrictive pattern. One had both airways obstruction and restriction. Two had a clinically significant response to bronchodilator and 12, including eight without airways obstruction on spirometry, had evidence of bronchial hyperresponsiveness on methacholine challenge testing. The prevalence of positive immunoglobulin E (IgE) to soy among Solae workers was five times greater than the prevalence among a group of comparison workers who were not occupationally exposed to soy, suggesting that immune recognition of soy among Solae workers resulted from occupational exposures. All asthma outcomes were significantly associated with immune response to soy, as measured by soy-specific IgE levels in the blood but not as measured by the skin prick test for soybean allergy. Concentrations of soy antigen and dust exposure were process-related. Compared to workers exposed to lower peak concentrations, those exposed to higher peak dust concentrations (measured by real-time sampling) were more likely to have spirometry indicating airways obstruction and to report work-related asthma-like symptoms. In addition, level of immunoglobulin G (IgG) to soy was associated with inhalable soy antigen level and work classification. Time-weighted-average inhalable soy antigen and dust concentrations were not associated with asthma outcomes in analyses involving all participants.