The authors review several approaches that show promise for predicting which antidepressant medication will be best for a particular patient and for achieving maximum benefit from each drug. These include delineation of clinical and historical characteristics associated with response to various drugs, use of psychological tests, assessment of biochemical and electroencephalographic parameters, evaluation of mood response to amphetamine, determination of acetylator status, and measurement of plasma tricyclic levels and degree of inhibition of platelet monoamine oxidase. The authors believe that the use of these approaches may improve our ability to help depressed patients.