The effects of short duration exposures to low concentrations of methyl-n-butyl-ketone (591786) (MBK) on a behavioral test were investigated using rats. Six male Sprague-Dawley-rats were tested daily on a multiple fixed ratio 5 fixed interval 3 minute schedule of reinforcement. Animals received either a saline (control) solution orally or, 1 day per week, MBK in concentrations of 68, 135, 270, or 406 milligrams per kilogram (mg/kg). Each rat's individual performance on the day of MBK administration was compared to his performance on the preceding day of saline administration. Each animal received all four MBK concentrations from 3 to 6 times per concentration over the 6 months during which MBK was administered. There were no permanent, overt clinical signs of weakness or foot drop in any rats. After 406mg/kg, some rats displayed sluggish movements and unsteadiness. The frequency of decrease in response rate to the stimuli after MBK administrations was 67 percent after 68 and 135mg/kg, 87 percent after 270mg/kg, and 86 percent after 406mg/kg. All animals showed decreases, but there were considerable individual differences in the severity of the deficit. The mean MBK response rate was significantly below the respective mean control rate at all four MBK concentrations. The mean percentage reduction in response rate was 20 percent at 68mg/kg, 30 percent at 135mg/kg, 40 percent at 270mg/kg, and 57 percent at 406mg/kg. No deterioration in performance occurred over the 6 month experiment; performance remained stable on saline days. Both fixed interval and fixed response interresponse times were increased as a function of MBK concentration. The authors conclude that MBK administration, at doses which did not produce clinical signs of neuropathy, affected response rate and interresponse time on both fixed interval and fixed response reinforcement schedules.