The experiments reported here were designed to determine if there are sex- and/or estrus cycle-dependent differences in amphetamine (AMPH)-elicited rotational behavior in unlesioned rats. Whole brain or striatal levels of AMPH produced by systemic administration of the drug were also measured. At all doses tested (1.0-10.0 mg/kg) systemic administration of AMPH resulted in significantly higher brain levels of AMPH in females than in males. A systemic dose was then calculated which produced equivalent brain levels of AMPH in males and females. Even with equivalent brain levels of AMPH, males produced significantly fewer net rotations than females in estrus, diestrus 2, or proestrus. In female rats the brain levels of AMPH produced by systemic administration did not vary with the estrous cycle. However, the amount of AMPH-elicited rotational behavior did. On the day of estrus, female produced significantly more net rotations than they did 24 h later, on the day of diestrus 1. It is suggested that sex and estrous cycle dependent differences in rotational behavior may be due to the direct or indirect modulation of mesostriatal dopamine activity by gonadal steroid hormone.