High-carbohydrate, high-fiber (HCF) diets have beneficial therapeutic effects for selected patients with diabetes mellitus. We have treated 10 patients with HCF diets on a metabolic ward and followed them for an average of 15 months while they were on maintenance diets at home. The HCF diets containing 70 per cent of calories as carbohydrate were accompanied by significant reductions in requirements for insulin or sulfonylureas. Fasting plasma glucose, serum cholesterol, and triglyceride values were significantly lower on the HCF diet than on a 43 per cent carbohydrate diet. On the HCF diet, insulin therapy was discontinued for five patients and sulfonylurea therapy for three. After an average of 15 months on the maintenance diet containing 55 per cent to 60 per cent carbohydrate, seven patients were still managed without insulin or sulfonylureas. Average fasting plasma glucose values during maintenance diets at home were identical to values on the HCF diets in the hospital. On the maintenance diet, serum cholesterol values were similar to initial values but serum triglyceride values were significantly lower than values on the 43 per cent carbohydrate diet. These studies indicate that moderately high-carbohydrate, high-fiber diets can be successfully followed at home and that improvements in glucose metabolism achieved in the hospital can be sustained outside the hospital.