Female rats are more active and explore more than males. In addition, females make fewer unreinforced responses on schedules which maintain low rates of responding (DRL). When general activity is high, subjects are more likely to engage in activities other than lever pressing. To test this hypothesis, male and female Wistar rats were trained to hold a response lever depressed for a minimum duration of 10 seconds. Reinforcement was delivered upon release of the lever. Females spent a significant smaller proportion of the total session time depressing the response lever than males. Differences between males and females in the number of unreinforced responses were not observed. Providing subjects with objects to promote collateral activities decreased the proportion of total session time subjects spent depressing the response lever for females, but not for males. An effect on the number of unreinforced responses was not observed.