Although a volume of literature concerned with the effects of tranquilizing drugs is accumulating, published reports of experimental or clinical trials with promazine hydrochloride are not numerous. Barsa and Kline1report a clinical effect similar to that found with chlorpromazine. Fazekas, Sullivan, and Schultz2; Mitchell5; Lemere,4and Usdin,6working mainly with a variety of acute psychiatric disorders, are in general agreement in reporting a positive clinical effectiveness of promazine therapy. The following paper, the first of a series, discusses a study completed at Ypsilanti State Hospital in which an attempt was made to assess scientifically the effects of one of the newer phenothiazine derivatives, promazine hydrochloride, on various aspects of patient behavior and on blood pressure, blood count, and bone marrow.* This paper gives the experimental design for the study and includes a report of the effects of promazine on the behavioral adjustment of patients.