The role of dopamine and serotonin release in limbic and striatal regions of the rat brain during various behaviors is investigated using an in vivo voltammetry technique. Carbon microelectrodes stereotaxically implanted in the caudate nuclei and nucleus accumbens measure neurotransmitter release concurrently with general locomotor activity and stereotyped behavior (gnawing, licking, biting) during normal circadian fluctuations, stress, and drug induced changes influencing dopaminergic transmission (amphetamine, neuroleptics) and serotonergic transmission (tryptophan, methysergide). Concentrations of dopamine and sertonin in tissue explants are measured by high performance liquid chromatography at the end of the experiment.