Abstract The use of phenformin in combination with other oral antidiabetic preparations was evaluated in 76 diabetic patients from the author's private practice and from the Diabetes Out-Patient Clinic of a community hospital. The indication for use of this combination was the presence of either primary or secondary failures with the preceding drugs used alone. In 135 clinical trials using either phenformin tablets or phenformin-TD capsules and another antidiabetic agent in varying doses the combination proved more efficacious than either drug alone. The most effective drugs combinations were those employing phenformin-aceto hexamide and phenformin-chlorpropamide. Even though 11 patients in this group taking combinations of phenformin with other oral agents required insulin to control the diabetes, many others were well regulated and the use of insulin thereby was obviated. The incidence of side effects in this series was negligible. However, the effectiveness of these more potent hypoglycemic agents enhances the possiblity of hypoglycemia which occurred in 9 instances. The patients must be thoroughly briefed on the importance of meals and interval feedings under all conditions.