Non-insulin dependent diabetes mellitus (NIDDM) is associated with chronic hyperglycemia, which increases the risk of developing microvascular and macrovascular complications. Elevated triglyceride (TG) and VLDL cholesterol levels and low levels of HDL cholesterol have also been frequently reported in NIDDM patients. A diet high in complex carbohydrate and low in fat is typically recommended for management of NIDDM, however, this has recently been challenged by scientific reports of the benefits of dietary intakes high in monounsaturated fat. Thirty-two individuals with NIDDM were randomized to receive either Ensure with Fibre (30% fat) or a high monounsaturated fatty acid product, Glucerna (50% fat). These products were consumed for 28 days at > 80% of daily energy intake. Post-treatment, dietary compliance was verified by a higher plasma TG 18:1 n-9 (p < 0.001) in the Glucerna group and a higher plasma TG 18:2 n-6 (p < 0.001) in the Ensure with Fibre group. The postprandial rise in blood glucose levels, determined by fingerprick samples, was significantly lower (p < 0.01) in the Glucerna group. Trends of clinical interest were greater mean decreases in the Glucerna group compared to the Ensure with Fibre group in: fructosamine, 9.13 umol/L vs 0.14 umol/L; glucose, 1.61 mmol/L vs 0.63 mmol/L; and insulin, 46.0 pmol/L vs 12.6 pmol/L; respectively. However, overall, fasting plasma glucose, fructosamine, TG and cholesterol levels were not significantly different between groups. Thus, in these patients, the high monounsaturated fat diet and the standard diet were similar with regard to usual indicators of carbohydrate and lipid metabolism. A high monounsaturated fat diet appears to pose no risk to lipoprotein metabolism in NIDDM patients.