A biological test was developed to determine the magnitude of an industrial exposure to methyl-chloride (74873) and to monitor physiological responses to different vapor concentrations and exposure durations. Male subjects were exposed to concentrations of for 1, 3, or 7.5 hours daily for 6 weeks, and female subjects were exposed to concentrations of 0 and 100ppm for the same time periods for 3 weeks. Methyl-chloride concentrations in the males fluctuated during the fifth week and resulted in a final 15 minute exposure concentration of 100ppm. A comprehensive medical examination was performed on each subject before and after the study. Alveolar breath samples and antecubital blood samples were drawn prior to and after exposures, and urine samples were collected twice a week. Neurological, cardiopulmonary function, cognitive, and physiological tests were conducted. Subjective responses were collected from the participants. Two male subjects, one each from the groups with 1 and 3 hour exposures, and one female from the 3 hour exposure group, had much higher breath levels of methyl chloride than the other subjects. Three male subjects, and one female, had grossly elevated breath methyl-chloride levels immediately after exposure. No deleterious, measurable effects of methyl-chloride exposure were observed. The authors recommend additional study to determine if different types of responders exist in industrial exposure situations, define the metabolites of methyl-chloride, and investigate the effect of exercise on different types of responders.