Morphine sulfate was injected in doses of 5, 10 and 20 mg/kg i.p. to male rats at 3:00 pm. At 4:00 pm, the rats were decapitated and norepinephrine, dopamine and serotonin levels were measured in seven brain regions (cortex, striatum septum, amygdala, hypothalamus, midbrain and pons). Growth hormone and corticosterone levels were assayed from plasma. Saline-injected animals served as controls. The only significant change in brain amine level was an increase in striatal dopamine which occurred after 5 mg/kg morphine. 20 mg/kg caused an increase in plasma corticosterone; lower doses were ineffective. The dose for maximum growth hormone release was 10 mg/kg, although all three doses were effective. It was not possible to relate changes in brain amine levels with these hormonal responses to acute morphine administration.