The adverse health effects of exposure to methyl-alcohol (67561) vapors in direct process, spirit duplicating machines were studied among teacher aides. Concentrations of methyl-alcohol vapor were measured for 15 minutes in the breathing zones of teacher aides as they operated 21 duplicators in 12 schools in a Washington school district. The sampling strategy covered a range of room sizes and available ventilation. Additional measurements were taken at six machines after adding NIOSH fabricated hood enclosures. A questionnaire covering symptoms of methyl-alcohol toxicity was completed by 66 female teacher aides and a comparison group of 66 female teachers. Death certificates and autopsy data were obtained for three deceased aides and examined for patterns consistent with methyl-alcohol effects. Methyl-alcohol concentrations at 21 duplicators, sampled without ventilation, ranged from 365 to 3080 parts per million (ppm) with a mean of 1060ppm; 15 machines exceeded the NIOSH short term ceiling of 800ppm. When 11 available ventilation systems were turned on, concentrations ranged from 80 to 1340ppm, with only one measurement exceeding 800ppm. When NIOSH enclosures were used, concentrations ranged from 9 to 130ppm, with only one measurement exceeding 800ppm. When NIOSH enclosures were used, concentrations ranged from 9 to 130ppm. Symptoms that were significantly more frequent in aides than teachers were blurred vision, headaches, dizziness, nausea, and skin problems. Based on symptom criteria, 45 percent of aides and 24 percent of teachers were classified as cases of methyl-alcohol toxicity. Among aides, the case attack rate increased with increasing time spent per week at the duplicating machine. No pattern suggestive of a common cause of death was found for the three deaths studied. The authors conclude that a potential health hazard is associated with the use of spirit duplicators. This hazard may be avoided by proper ventilation.