Four rats lever pressed for food on a two component multiple FR-VI schedule of reinforcement. In the FR component a brief electric shock coincided with the presentation of food. After level pressing stabilized in the presence of the shock, drugs were administered in two phases. In Phase 1, one of four doses of either gamma-butyrolactone or sodium pentobarbital was injected before sessions. Both drugs increased lever pressing rates during the shocked component of the schedule at doses which did not affect lever pressing rates during the unshocked component. In Phase 2, one of four doses of a mixture of the two compounds was injected. The drug mixture increased rates of punished lever-pressing to levels similar to those reached in Phase 1. These results confirm previous findings for sodium pentobarbital and indicate that gamma-butyrolactone warrants further investigation into its behavioral properties.