The authors describe a longitudinal, placebo-controlled study of the response to drug treatment of a 62-year-old schizoaffective patient hospitalized for 40 years. While neither lithium nor a neuroleptic drug alone was effective, both drugs administered simultaneously led to the gradual extinction of a pronounced behavioral cycle and the disappearance of manifest psychosis. The authors suggest a synergistic interaction between the two drugs and stress the need for sustained trials of the combination in patients with similar behavioral cycles.