A 100-gm., two-hour, oral glucose tolerance test was given to an institutional group of 359 mentally ill men under age fifty without known diabetes. The test was selectively repeated. In 11.7 per cent of the group, results were interpreted, in association with other data, as being consistent with previously unknown, unsuspected diabetes. It occurred more frequently among the older, the overweight and those with diabetic relatives, resembling the prevalence of known diabetes in the general population. The relatively high incidence of previously unknown diabetes that was discovered in the group is ascribed to their age range, commonness of overweight and the method of study.
Further investigation is required to determine if prolonged phenothiazine therapy may be a contributory diabetogenic influence.