The status of the enzyme monoamine oxidase B (MAO-B) was directly evaluated in the postmortem brain from 20 alcoholics and 23 matched controls. The density of MAO-B sites was quantified by the specific binding of the selective inhibitor [3H]Ro 19-6327 (lazabemide) (8 nM) to cortical membranes. A positive correlation between age at death and MAO-B density was observed in the total sample (r = 0.37, p = 0.015). The density of MAO-B in alcoholics (Bmax = 1,263 +/- 131 fmol/mg of protein) was not different form that in control (Bmax = 1,131 +/- 96 fmol/mg of protein). Ethanol in vitro inhibited [3H]Ro 19-6327 binding, with similar potency in membranes form alcoholics (Ki = 280 +/- 13 mM) and controls (Ki = 338 +/- 84 mM). The present results in brain tissue contrast with previous reports of decreased MAO-B enzymatic activity in platelets of alcoholics, but strongly agree with recent genetic studies on MAO-B status in alcoholism.