Rats were given chronic treatments with ethanol in two ways: by offering 10% ethanol in water as the only liquid supply for 34 weeks and by exposing the rats to ethanol vapour during 5 h daily for 7 weeks. In this way blood ethanol levels of 1.4-2.3 and 5.5-6.9 mg/ml, respectively, were accomplished. In neither of the cases was brain monoamine oxidase activity changed. The result supports an hypothesis previously advanced that the lowered monoamine oxidase activity found in the brain of a suicide patient was not due to a direct effect of ethanol on alcoholics in the suicide group, but that the low enzyme activity reflected a low monoaminergic activity in the brains of the patients in the suicide group.