Background. To evaluate the possible benefits of the addition of intermediate-acting insulin administered at bedtime to therapy with daytime sulfonylureas in patients with non-insulin-dependent diabetes mellitus for whom maximal doses of oral hypoglycemic agents have not been successful. Methods: Study subjects were 16 consecutive obese patients aged from 44 to 78 years (mean age, 62 years) with histories of non-insulin-dependent diabetes mellitus for a mean of 9 years. None of the subjects had been able to control their diabetes with maximal doses of oral hypoglycemic agents. All patients received 20 mg glipizide or 10 mg glyburide twice a day, as well as education about the American Diabetes Association diet. Neutral protamine Hagedorn (NPH) insulin was empirically added in doses from 0.1 to 0.2 units/kg given at bedtime. The dose was adjusted on the basis of fasting blood glucose levels. Results: Mean fasting blood glucose decreased from 13.7 +/- 3.4 to 8.3 +/- 2.7 mmol/L at 3 months and 7.3 +/- 2.0 mmol/L at 1 year. Glycosylated hemoglobin decreased from 9.0% +/- 1.9% to 6.2% +/- 1.16% at 3 months and 6.3% +/- 1.22% at 1 year. Conclusion: A late-night dose of NPH insulin was added to a regimen of daytime sulfonylureas in a group of obese patients with type II diabetes whose hyperglycemia was not controlled with maximal doses of oral hypoglycemic agents. This treatment proved to be beneficial and is a useful alternative to conventional insulin therapy in this group of patients.