This paper concerns sequential effects in choice reaction time tasks. Performance in two interleaved auditory tasks was examined, and two general types of sequential effects were revealed. First, a response repetition effect occurred: Subjects were facilitated in responding when both the stimulus and the response were immediately repeated. Generally, it appeared that subjects were operating according to the bypass rule--that is, repeat the response if the stimulus or some aspect thereof is repeated from the preceding trial; otherwise, change the response. In addition, the experiment also revealed a second type of sequential effect, known as a task-switching effect Subjects were overall slower to respond when the task changed between adjacent trials than when there was no task change. A final result was that subjects were markedly impaired when the stimulus changed but the same response had to be repeated. This finding has been reported elsewhere when purely visual tasks have been used. Hence, it seems that particular difficulties arise, in such sequential testing situations, when type-distinct stimuli are grouped into the same response categories.