Norepinephrine (NE), dopamine (DA), tyrosine hydroxylase (TH), catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO) levels were measured in human brain tissue obtained at autopsy from a series of 39 patients dying of various medical and accidental causes. The nine following brain areas were studied: globus pallidus, thalamus, hypothalamus, hippocampus, substantia nigra, floor of the fourth ventricle, orbital cortex, caudate nucleus, and mammillary bodies. Enzyme activity correlated positively with age in all brain areas for MAO (with both benzylamine and tryptamine substrates) but no consistent pattern of correlation was found for COMT and TH. Mean MAO activity was significantly higher in women than men. There is increased brain MAO activity during late childhood and adolescence. These data are consistent with previous evidence suggesting that age and sex are important determinants of amine metabolism in the human central nervous system.