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Aspects of carbohydrate and lipid metabolism were studied in 50 nondiabetic African subjects living in Johannesburg. Twenty-six of them were overweight, invariably associated with a high-carbohydrate intake. In general, the obese group demonstrated significantly raised serum insulin levels, normal glucose tolerance, normal fasting serum triglycerides, and significantly elevated serum cholesterol concentrations. However, the degree of obesity was not significantly correlated with any of these metabolic variables--notably basal or stimulated insulin levels. This suggests that the obese state, per se, was not the major cause of the hyperinsulinemia, and that other factors influenced individual insulin responses or sensitivity. Inconsistently excessive dietary carbohydrate ingestion and an unusual degree of physical activity may have been important. A striking correlation emerged between fasting serum triglycerides and insulin concentrations (both basal and stimulated); the possibility that this reflects acceleration of hepatic triglyceride synthesis by insulin is discussed. The concept of obesity invariably producing insulin resistance and progressive compensatory hyperinsulinism may not apply in all environmental conditions.