The National Institute for Occupational Safety and Health (NIOSH) received a request for a health hazard evaluation (HHE) from Superior Label Systems, Inc. (SLS) in Mason, Ohio, on January 24, 2001. The request stated that employees in the line division of the plant were experiencing intermittent blurred vision, and that one employee had been evaluated by an ophthalmologist who found a "film over his eyes." Employees in the prime division of the plant were not experiencing visual disturbances. Workers and management had not been able to associate these visual changes with any particular substance in use. A site visit was conducted on February 8, 2001, that included an opening meeting with management and employee representatives, an overview of the process, and a walk-through of the plant. Medical questionnaires, eye exams, and extensive industrial hygiene monitoring for two types of tertiary amine compounds, dimethylisopropanolamine (DMIPA) and dimethylaminoethanol (DMAE), were performed from April 23-26 and April 30-May 3, 2001. Eighty-nine percent of line workers reported having experienced blurry vision while at work in the past 12 months, compared to 12.5% of prime workers (p<0.01). Findings were similar for halo and blue-grey vision. Forty-seven percent of those reporting blurry, halo, or blue-grey vision experienced eye irritation along with the visual changes, 44% reported difficulty performing their job due to the visual changes, and 39% reported difficulty driving home due to vision problems. A total of 108 full-shift personal breathing-zone (PBZ) air samples for the amines were collected, 93 in the line division and 15 in the prime division. The mean time-weighted average (TWA) concentration of DMIPA was significantly higher in the line division than in the prime division (7.70 mg/m3 vs. 2.08 mg/m3, p<0.01), as was the mean TWA concentration for total amines (9.96 mg/m3 vs. 5.56 mg/m3, p<0.01). The mean TWA concentration of DMAE was higher in the prime division than the line division (3.47 mg/m3 vs. 2.27 mg/m3, p<0.01). There was a positive association between reported visual symptoms and concentrations of total amines. Higher levels of total amines were associated with increased risk of reporting blurry vision (odds ratio [OR]=1.78, 95% confidence interval [CI]=1.41, 2.26), halo vision (OR=1.38, 95% CI=1.20, 1.58), and blue-grey vision (OR=1.77, 95% CI= 1.31, 2.39). All OR reported refer to a per unit increase of 1 mg/m3 in amine concentration. Symptom reporting increased with exposure to increasing concentrations of amines. The risk of corneal opacity rose with increasing exposure to total amines (OR=1.15, 95% CI= 1.02, 1.30). The prevalence of corneal opacity also increased with increasing concentration of total amines. The prevalence of increased corneal thickness in either eye increased with higher levels of exposure to total amines, as did both the mean and median changes in thickness. Median corneal thickness increased with increasing grades of corneal opacity. There was a statistically significant relationship between total amine concentration and increased risk of reduced bilateral visual acuity and 2.5% contrast sensitivity (OR=1.2, 95% CI=1.001,1.43; OR=1.28, 95% CI=1.14,1.43, respectively). At the time of the site survey, NIOSH investigators notified SLS management that the pH adjuster may be responsible for workers visual complaints. SLS management promptly began to dilute the pH adjuster, which contains DMIPA, with water. This action resulted in a resolution of visual complaints among the workers. Exposure to tertiary amines at SLS was found to be associated with visual and ocular changes. While this appears to be a reversible phenomena, these visual changes pose a safety hazard, both on the job and when driving home. Recommendations include: (1) continuing to dilute the pH adjuster; (2) covering all 5-gallon ink pails to reduce the amount of chemicals vaporizing into the work environment; and (3) improving local exhaust ventilation at printing presses.