During the course of studies of hypertensive patients, including a double blind study, observations were made concerning the diabetogenic activity of benzothiadiazine derivatives. This activity was observed to occur in nonobese patients without a family history of diabetes as well as in obese hypertensives with such a family history. These observations suggest that benzothiadiazines should not be given to young or middle-aged hypertensives in whom there is a lengthy life expectancy and for whom alternative hypotensive therapy is feasible.