In addition to hypothalamic sites known to contain LHRH, several extrahypothalamic structures in both male and female rats were discovered to contain the decapeptide. In the mesencephalon, the fasciculus retroflexus, interpeduncular nucleus and midbrain central grey contained readily detectable quantities of LHRH. Single neurons responsive to microiontophoretically applied LHRH were also discovered in the mesencephalon suggesting a physiological role for the decapeptide in neuronal events at the level of the midbrain.