Although phenothiazines have gained acceptance as the standard treatment for the acute episode of schizophrenia (Rathod and Rees, 1953; Cole, 1964), there is much more doubt about their effectiveness as maintenance therapy. Several American studies have reported on the results of maintenance therapy with chlorpromazine compared with placebo, and found phenothiazine treatment to be superior in preventing relapse (Scarpitti et al., 1964; Pasamanick et al., 1957; Ravaris et al., 1967). However, these studies suffer from methodological problems which impair their clarity. First, as emphasized by Leff and Wing (1971), diagnostic criteria are rarely stipulated. This is clearly important if American work is to be compared with British, since Kendell et al. (1971) have shown the wider concept of schizophrenia used in the U.S.A. Secondly, the likelihood of bias occurring in the population meeting trial selection criteria, resulting in a trial population which is unrepresentative of the group as a whole, is not usually defined. Every trial worker knows this ‘shrinking sample’ phenomenon, which appears to result in a sudden scarcity of patients as soon as a trial is contemplated. The trial of maintenance therapy conducted by Leff and Wing (1971) meets this objection by following the progress of patients who met the trial criteria but could not be included for various other reasons.