The results are reported of a double-blind controlled trial of a recently introduced major tranquilizer thiothixene (Navane, Pfizer) against chlorpromazine in 24 chronic schizophrenics in the Royal Edinburgh Hospital, Edinburgh, Scotland. Additionally, a limited experiment in withdrawal of routine tranquilizers in these patients (one month) was carried out prior to the trial. Changes in manifest psychosis (symptoms) and social disability were assessed by the use of the Lorr scale (IMPS) and the Nurses' Observation Scale for Inpatient Evaluation (NOSIE) at suitable intervals. The results indicated that thiothixene conferred no advantage over chlorpromazine in symptom relief or social improvement. Serial measures showed no significant change in these patients as a group when on active drugs as opposed to placebo, or with the course of time. 12.5% of patients relapsed during the placebo period: these patients were younger than the non-relapsers and had received larger daily doses of phenothiazines prior to the trial.