Prolactin administered systemically, intracerebroventricularly or locally into the lateral hypothalamus enhances rapid eye movement sleep (REM) when given diurnally and decreases REM when given nocturnally. The amygdala is being recognized as an important modulator of behavioral state, and the central nucleus of the amygdala (CNA) has a high concentration of prolactin fibers and receptors. We microinjected prolactin (10, 100, 250 ng/0.2 microliter saline) or saline alone into CNA of rats and measured the effect on behavioral state. Prolactin produced a dose-dependent decrease in non-REM (NREM), with the effect becoming significant at the high (250 ng) dose. REM was not significantly affected at any dosage. The results indicate a role for prolactin in CNA in the control of NREM. The results are discussed in terms of the amygdala having a broad role in the regulation of behavioral state.