Two-component schedules of differential-reinforcement-of-low-rate were presented, where the contingencies specified separately two minimum interresponse times, t(1) and t(2), required for reinforcement, depending on whether the interresponse time was initiated by, in one case, a reinforced response (t(1)) or, in the other, a nonreinforced response (t(2)). A distinctive pattern of responding developed on each of the two contingencies. Duration of an interresponse time approximated t(1) when the t(1) contingency was in effect, and t(2) when the t(2) contingency was in effect. This relationship persisted even when t(2) was shorter than t(1), and responding at a higher rate on the t(1) contingency would have greatly increased the rate of reinforcement. Increasing the value of t(2) resulted in both longer interresponse times on the t(1) contingency, and a higher probability of a response-burst on those occasions when the contingency switched from t(1) to t(2). The results indicated that both reinforced and nonreinforced responses functioned as discriminative events in determining the duration of following interresponse times.