There is considerable evidence that opiates and opiate peptides produce their various effects by interacting with mu, delta an/or kappa opioid receptor types. The specificity of these receptor types for mediating specific pharmacological effects, especially euphoria and pain relief are of major importance in understanding the abuse potential and the analgesic action of these agents. In order to compare the roles of these various opiate receptors in mediating various pharmacological actions, the relative potencies of the effects of a variety of opiate ligands and peptides will be determined on four procedures, each modeling a different putative action will be determined. These procedures consist of the determination of (1) the threshold for rewarding intracranial stimulation, a model for drug-induced euphoria, (2) the threshold for detecting stimulation, a model for drug-induced analgesia, (3) the threshold for detection of intracranial stimulation that is neither rewarding or aversive, a model for assessing the effects of drugs on perceptual/attentional function and, (4) the self administration of drugs, a model of the reinforcing effects of abuse substances. All experiments will be carried out in male F-344 rats.