Phenylethylamine (PEA), an endogenous neuroamine, increases attention and activity in animals and has been shown to relieve depression in 60% of depressed patients. It has been proposed that PEA deficit may be the cause of a common form of depressive illness. Fourteen patients with major depressive episodes that responded to PEA treatment (10-60 mg orally per day, with 10 mg/day selegiline to prevent rapid PEA destruction) were reexamined 20 to 50 weeks later. The antidepressant response had been maintained in 12 patients. Effective dosage did not change with time. There were no apparent side effects. PEA produces sustained relief of depression in a significant number of patients, including some unresponsive to the standard treatments. PEA improves mood as rapidly as amphetamine but does not produce tolerance.