The effects of reinforcement and punishment on response suppression under variable-interval reinforcement and variable-ratio punishment schedules were investigated. At baseline, lever pressing in rats was maintained by a variable-interval food reinforcement schedule. In the punishment condition, responding was punished by a grid shock under a variable-ratio schedule in which three rats experienced four or five punishment rates and a fixed reinforcement rate. Results indicated that there was a negative linear correlation between the variable-ratio punishment rate and the response rate. Results of three rats that experienced five or six reinforcement rates with a fixed punishment rate indicated that punishment suppressed responding at all reinforcement rates. These findings suggest that the punishment rate was strongly related to response suppression under both variable-interval reinforcement and variable-ratio punishment schedules.