The relative efficiency for the release of luteinizing hormone (LH) and prolactin after anodal and cathodal stimulation applied within the preoptic-suprachiasmatic region (POA-SCH) was studied in adult male rats under pentobarbital anesthesia. Single monopolar pulses 0.5 ms duration, 100 or 200 microA intensity, were applied within the dorsal [vertical (V) 7.3] or ventral (V 7.8 to 7.9) aspects of the POA-SCH at a mean rate of 10 Hz in 30-s trains every other 30 s for a period of 30 min. Blood samples were obtained at 30-min intervals starting immediately before onset of stimulation. Although there were no obvious effect on plasma LH titers, prolactin concentrations tended to be higher when cathodal stimulation was applied at V 7.9 and when anodal pulses were applied at V 7.3. Stimulation with paired twin pulses (1.0 ms duration, 20.0 ms intrapair interval) resulted in clearer hormonal effects, namely, a significant increase in plasma prolactin concentration at 30 min only when cathodal stimuli were applied to the ventral aspect of the POA-SCH. Plasma LH concentrations were higher also at 30 min in the same experimental group, although the increase was not statistically significant. These results indicate the effectiveness of cathodal stimuli to induce hormonal release when applied within the ventral half of the POA-SCH in male rats. Present results suggest the existence of predominantly facilitatory neural elements for the release of prolactin (and LH) in this brain region.