The contents of monoamine neurotransmitters and metabolites were assayed in the frontal cortex, nucleus accumbens and anterior striatum of rats from the selectively bred alcohol-preferring P and nonpreferring NP lines. Lower levels of serotonin (20-30%) in all three brain regions of P as compared with NP rats lends support to the hypothesis that a decreased metabolic activity and/or innervation by serotonin neurons is associated with the abnormally high volitional intake of ethanol. Of additional interest, however, were the approximately 25% lower contents of dopamine and its major metabolites in the nucleus accumbens of the P rats. This observation may indicate that P rats have a specific deficiency in the dopaminergic projections from the ventral tegmental area to the nucleus accumbens and, since the accumbens is an important structure in brain reward circuitry, it might also be an important determinant of the excessive volitional intake of alcohol by P rats.