A multineurotransmitter neuronal system that synthesizes and secretes both acetylated and deacetylated forms of alpha-melantropin and beta-endorphin is present in rat and human brain. The N-acetylated from of alpha-melanotropin had more potent behavioral effects than the deacetylated alpha-melanotropin. In the case of beta-endorphin, however, the deacetylated form has been shown to be more potent than the acetylated form. Enzymatic N-acetylation appears to be an important regulatory process for modulating the behavioral activity of peptides secreted from the opiomelanotropinergic multineurotransmitter neuron.