Post-reinforcement pauses (PRP) and interresponse times (IRTs) were examined to determine if these two temporal units changed in a similar fashion as a function of the delivery of differential reinforcement. Two experiments were conducted. In Experiment 1, four pigeons were exposed to a series of procedures in which PRP and IRT durations were gradually increased and then decreased. A fixed-ratio two (FR 2) differentiation schedule was used. Reinforcement was delivered if the PRP or IRT durations were greater than (PRP > and IRT > procedures) or less than (PRP < and IRT < procedures) specified temporal criteria. Criteria were gradually changed across procedures. Results showed that PRPs and IRTs changed in accordance with the differential reinforcement as specified by the various contingencies. When PRPs and IRTs were free to vary, the PRPs tended to change in a direction consistent with the IRT shaping contingencys whereas, the IRTs tended to shorten regardless of the PRP shaping contingency. In Experiment 2, two subjects were exposed to both an FR 2 and FR 1 schedule to determine if schedule size influenced the effects obtained on the differentiation procedures. PRPs were systematically changed using a differentiation procedure with a response requirement of either FR 1 or FR 2. Results showed similar changes in PRP durations between FR 1 and FR 2 differentiation procedures. An analysis of errors made on each shaping condition in both experiments was conducted to determine whether PRPs or IRTs were more susceptible to the differential reinforcement contingencies. Fewer errors were made on the PRP shaping conditions, indicating that PRPs were more easily changed. Implications for a comprehensive theory of reinforcement were discussed.