Discrete trial procedures permit exact control or description of the time of occurrence of stimuli, the probability of response occurrence, and the patterning of responses. They also make possible the experimental manipulation of the composition of the stimuli controlling behavior. The use of discrete trial procedures is illustrated here in an examination of the effects of scopolamine, a representative cholinergic blocker, on several aspects of behavior: Memory. Response alternation experiments, in which the spacing of discrete trials varies within the experimental session, show that, whereas accuracy of responding is consistently poorer under drug, the decline of accuracy with time since last trial is similar for drugged and nondrugged animals. Thus the drug does not affect memory "storage". Inhibition. Experiments in which discrete trials are presented in pairs, such that the correct response on Trial 2 of the pair is contingent upon Trial 1 events, show how the "disinhibiting" effect of scopolamine (as indicated by enhanced responding on "no go" trials) is augmented by increasing the time gap between Trial 1 and Trial 2, or by minimizing controlling stimuli on Trial 1. Discrimination. A variety of experiments suggest that scopolamine decreases the "detectability" of stimuli. Detectability effects, along with disinhibition observed under certain specific conditions, constitute the prinicipal behavioral actions of scopolamine observed with discrete trial procedures.