This study was designed to examine the relationship between regional levels of brain amines (norepinephrine, NE; dopamine, DA; serotonin, 5-HT) and plasma hormone levels (corticosterone, CS; growth hormone, GH) in rats following chronic morphine administration (40 mg/kg twice daily). Rats were sacrificed at 4:00 pm (and the final injection was made at 9:00 am). Amine and hormone levels were determined after 1, 2 and 6 weeks of daily injections of morphine. Increased plasma CS was found after 1 and 2 weeks of injections and decreased GH levels were present after 2 and 6 weeks. In another 2 week study when morphine was administered 1 hr before sacrifice, plasma levels of CS were decreased and GH increased. Serotonin levels were decreased in all brain regions after 2 and 6 weeks of morphine administration and DA was decreased in the amygdala after 6 weeks. In 2 weeks treated rats injected 1 hr before sacrifice 5-HT levels had returned to control levels and DA was decreased. Inverse correlations were found to relate with 5-HT and CS levels, CS with GH levels and GH with brain DA. A direct correlation was present in GH and 5-HT levels.