During Phase I, three female human subjects pressed a button for monetary reinforcement in five variable‐interval schedules specifying different frequencies of reinforcement. On alternate days, responding was also punished (by subtracting money) according to a variable‐ratio 34 schedule. In the absence of punishment, response rates conformed to Herrnstein's equation for single variable‐interval schedules. Punishment suppressed responding at all frequencies of reinforcement. This was reflected in a change in the values of both constants in Herrnstein's equation: the value of the theoretical maximum response‐rate parameter was reduced, and the parameter describing the reinforcement frequency corresponding to the half‐maximal response rate was elevated. During Phase II, the same five schedules (A) were in operation (without punishment), but in addition, a concurrent variable‐interval schedule (B) of standard reinforcement frequency was introduced. On alternate days, responding in Component B was punished according to a variable‐ratio 34 schedule. In the absence of punishment, absolute response rates conformed to equations proposed by Herrnstein to describe performance in concurrent schedules; the ratios of the response rates in the two components and the ratios of the times spent in the two components conformed to the Matching Law. When responding in Component B was punished, response rates in Component B were reduced and those in Component A were elevated, these changes being reflected in distortions of the matching