Humans were used to investigate changes in response force occurring soon after reinforcement was eliminated. In Experiment 1, in a 300-s baseline phase, 10 participants received a point for holding down a pressure sensor set to operate at a force equal to 85% of the maximum force the participants exerted during a pretest. Following this, during a 600-s extinction phase, criterion responses had no consequence. In Experiment 2, 6 participants worked on the same task, but (a) points were exchangeable for money and (b) after extinction, the reinforcement baseline phase was reinstated. In Experiment 3, 6 participants completed the same task as in Experiment 2, but the required minimum force was 60% of the maximum force exerted during the pretest. In each experiment, increases in response force relative to the mean and peak force exerted during the last 100 s of baseline were observed in most participants when force responses were aggregated into short sample intervals, but less so with longer ones. The increases, however, were not systematic across or within participants, questioning the generality of and the criteria for demonstrating an extinction burst.