OBJECTIVE - To examine the effects of a high-carbohydrate low-fat (HCLF) and a modified-fat (MF) diet on body weight and metabolic control in subjects with non-insulin-dependent diabetes mellitus (NIDDM) living at home. RESEARCH DESIGN AND METHODS -Twenty-four NIDDM patients followed HCLF and MF diets alternately and in random order for a 3-month period while at home, with a 1- month baseline and washout between diets. Before and after each diet, fasting glucose and lipids, HbA(1c), blood pressure, and body weight were measured. Dietary preferences were assessed by questionnaire. RESULTS - Subjects consumed 50% of energy as carbohydrate and 23% as fat on the HCLF diet and 40% of energy as carbohydrate and 36% as fat (over half of which was monounsaturated fat) on the MF diet. Subjects lost weight on both HCLF and MF diets (mean loss 0.7 and 1.3 kg, respectively). Although the MF diet resulted in a small decrease in fasting glucose levels, there was no significant change in HbA(1c). Similarly, there was no significant difference between the diets in changes in blood pressure or fasting blood lipids. Most subjects (65%) preferred the MF diet. CONCLUSIONS - Although the MF diet is not a low- fat diet, it did not appear to facilitate weight gain in subjects with NIDDM living at home. The MF diet provides an alternative for individuals unable to comply with HCLF diets.