We determined whether the response of thyrotropin (TSH) to thyrotropin-releasing hormone could predict the outcome of treatment with antidepressant and neuroleptic drugs. We studied 114 female patients diagnosed as having major and minor depressive, manic, schizoaffective, and schizophrenic disorders. A blunted TSH response (less than 5 microU/mL [less than 5 mU/L]) at admission was associated with recovery after nine weeks of inpatient treatment using clomipramine hydrochloride for depression and haloperidol for psychosis. A blunted TSH response at discharge was associated with early relapse in depressives receiving clomipramine maintenance therapy. Our findings support the notion that the thyrotropin-releasing hormone test is a "state" marker that may be of use in predicting the outcome of treatment with antidepressant and neuroleptic drugs.