This study investigated the differential effects of chronically administered nicotine and saline on motor activity in the rat. Nicotine was administered via a subcutaneously implanted osmotic minipump to effect an 8 hour off, 16 hour on, flow. Subjects were 48 male and 48 female albino rats, each about 165 days old. Activity was monitored every hour for 192 consecutive hours. Results indicated that the female animals were more active than the males, and that animals receiving nicotine were significantly more active on the first two days of drug administration than control animals; however, by the fourth day there were no significant differences between the activity levels of animals that received nicotine and those of control animals.