1. By study of the synthesis and turnover of brain monoamines and with the use of behavioral models which indicate the functional activity of brain 5HT and dopamine, it is possible to unravel the mechanisms by which some drugs produce behavioral effects. 2. Using these techniques the acute and chronic effects of certain neuroleptics, propranolol and other beta-adrenergic blocking agents, repeated electroconvulsive shock, and lithium upon the functional activity of brain 5HT and dopamine are examined. 3. The clinical relevance of these studies is discussed.