Three trained Ss participated in a choice reaction time task under conditions of 0, 1, 2 and 3-bits of stimulus uncertainty. Stimuli were presented in random sequence. Prior to each presentation Ss were required to state a behavioral hypothesis, i.e., guess which stimulus event would occur. The stimulus uncertainty-choice reaction time relationship was linear, confirming previous findings. However, when correct and incorrect behavioral hypothesis trials were separately analyzed, it was found that the positive linear relation was obtained only in the latter case; choice reaction time was independent of stimulus uncertainty when S’s guess was correct.