The authors reviewed relevant studies in an attempt to define the onset and time course of antipsychotic effects of neuroleptic drugs. After excluding open trials, studies of chronically psychotic patients, and studies not using a placebo or nonneuroleptic sedative as a control, they found only five reports suitable for analysis. Among these, the degree of patients' improvement during neuroleptic treatment was similar regardless of the duration of the study. Also, in studies comparing neuroleptics with sedatives, similar improvement was observed with both treatments. Although neuroleptic drugs have been used clinically for 35 years, the timing of their specific therapeutic effects remains unclear.