A double-blind comparison was conducted using typical doses of soporific agents from three drug classes and a placebo. Drugs which were used in the study included secobarbital, flurazepam hydrochloride, and thioridazine. Subjects were 40 outpatient volunteers whose primary complaint was difficulty in falling to sleep. Subjects were randomly assigned to one of the three drug groups or the placebo group. One of the drugs or the placebo was administered to each subject for 3 nights. Half of the subjects in each of the four groups were told the drug had caused any observed changes in their sleep behavior and were in this way led to attribute any changed sleep behavior externally to the drug. The other half were told the drugs were not typically used to treat insomnia and changes in their sleep were due to changes made in their own behavior, thus attributing any changes in sleep behavior internally. The implication for clinicians was that a short course of drug therapy using a placebo or one of several soporific drugs might be used equally effectively to treat primary latency insomnia. Additionally, the results demonstrated that clinicians might expect the effectiveness of treatment to be maintained following treatment. Recommendations included a suggestion for future research with soporific drugs in other classes.