Dopamine and its specific receptors are widely distributed in man. Body regions where dopaminergic activity is of special pharmacologic interest include the basal ganglions, hypothalamus, chemoreceptor trigger zone, other less well defined areas in the central nervous system, and the renal and cardiovascular systems. The search for dopaminergic agents to modify these systems in disease states has depended heavily on in vitro and in vivo bioassays. These assays involving receptor binding, enzyme activation, smooth muscle and neuronal excitation, and modification of animal behavior have provided physicians with important therapeutic tools. Indeed, the introduction of levodopa for the treatment of Parkinson's disease and of the phenothiazines and related drugs for schizophrenia and psychosis has been a hallmark of neuropharmacologic research. However, the maximal benefits that these drugs may afford have not yet been realized due to an inadequate understanding of disease processes and a relative lack of specificity of drug action.