Experiments are proposed in four areas relating to the stimulus properties of drugs. Project 1 seeks to improve the utility of the drug discrimination procedure so as to enhance its utility as a preclinical research method by identifying training procedures which will yield results more accurately representational of underlying drug effects than do the results of present drug discrimination procedures. Project 2 seeks to identify the type of mechanism responsible for state dependent learning. The threshold dosages that are required to produce drug discriminations and state dependent learning will be determined. Comparison of these thresholds should demonstrate whether or not sensory events underlie both phenomena. Project 3 will investigate the degree to which behaviors learned in the no drug condition become contingent upon interoceptive cues present in that condition. Theory and experimental results presently disagree on this issue, which leads to incorrect interpretation of experimental results and hinders attempts to improve the drug discrimination procedure. Project 4 will investigate whether drugs can become conditioned stimuli in classical conditioning paradigms, thus acquiring conditioned reactions that may augment or interfer with the usual effects of the drugs. Experiments are proposed to determine the ease of formation of such conditioned reactions to drugs, the variety of situations in which they occur, and the rapidity with which they extinguish. A total of ten separate experiments are proposed.