The nucleus accumbens is an important telencephalic region, which is the target limbic and mesolimbic pathways. Because of an ongoing physiological study of the effects of dopamine, we wanted to determine regional differences of dopamine and norepinephrine concentrations in the nucleus. As determined by radioenzymatic assays, dopamine levels were not significantly different in the anterior-posterior dimension, averaging approximately 187 ng dopamine/mg protein. Substantial amounts of norepinephrine were found throughout the nucleus, but the levels were significantly higher in the caudal portions of the nucleus, being approximately 4.5 times higher than in the anterior portions.