Visual disturbances among employees at a flexo-printing company prompted its managers to request assistance from the National Institute for Occupational Safety and Health (NIOSH). The facility prints labels on paper or plastic using water-based, UV-cured, and fluorescent inks. The plant had approximately 100 employees working as press operators, rewinder operators, and press assistants. The facility was divided into two printing areas: the line division (approximately 15,000 sq ft) and the prime division (approximately 9,000 sq ft). Although adjacent to one another, the divisions were separated by a concrete wall and flexible-strip doorway curtains. Line-division employees were reporting eye problems. This division had eight high-speed (400-ft/min) printing presses and used primarily water-based inks for printing less detailed labels, such as those on milk and orange juice containers. Fluorescent inks were used occasionally; UV inks were not used. Prime-division employees were not reporting vision problems. This division had seven lower-speed (150- to 175-ft/min) printing presses and primarily used water-based inks to print detailed labels, such as those on cosmetics and automotive products. Fluorescent and UV inks were used in this division. Both divisions used 5-gal pails for holding inks before pumping the inks into troughs. Managers reported to NIOSH that line-division employees were experiencing intermittent blurred vision at work. One employee was evaluated by an ophthalmologist who found a "film over his eyes". Employees said their blurred vision was like looking through a fog or mist. The effect was most noticeable when looking at lights, causing a halo. Vision changes typically resolved within a couple of hours after leaving work. However, it was difficult for employees to do their jobs and drive home safely. Symptoms were unpredictable, but they seemed to be increasing in frequency. Employees and managers were unable to associate these visual changes with use of a particular substance, but noticed that symptoms were only reported by line-division employees and only on Mondays through Thursdays, when production activity was highest. After meeting with management and employee representatives, our team monitored the air for chemical exposures and assessed the exhaust ventilation system. We sampled in both divisions to identify air contaminants unique to these production areas. We surveyed employees using a medical questionnaire and performed eye exams on line-division employees and any prime-division employees who had experienced visual disturbances in the past. Eye exams were conducted at the beginning and end of work shifts for one week. We found an association between visual symptoms and exposure to two chemicals: dimethylaminoethanol (DMAE) in the water-based ink and clean print additive (used to lengthen drying time so the ink did not dry too quickly) and dimethylisopropanolamine (DMIPA) in the pH adjuster. DMAE and DMIPA belong to a class of chemicals called tertiary amines.