The effects of microiontophoretic application of luliberin (LHRH), norepinephrine (NEO) and morphine on activity of the medial preoptic hypothalamic neurons were studied in male rabbits. About 80% of all the neurons responded to LHRH, mainly with facilitation. NEO appeared to have inhibitory influence on the LHRH-induced effects, when LHRH was applied simultaneously with NEO. Since the LHRH effect might be mediated via opiate receptors, it was examined against the background of morphine application. LHRH applied after morphine increased the number of unresponsive units. During simultaneous application of LHRH and morphine the number of unresponsive units increased by 30% and the number of facilitation responses decreased to 30% of the neurons under study. These findings confirm that the opiate receptors and noradrenergic system play a certain role in the central effects of LHRH.