The influence of elevated levels of oleate on insulin-stimulated 3-0-methylglucose transport was assessed in vitro, in isolated skeletal muscle obtained from patients with type 2 (non-insulin-dependent) diabetes mellitus (n = 7) and control subjects (n = 8). An increase in oleate levels from 0.3 to 1.0 mmol/l induced a 3.7-fold increase in the rate of oleate oxidation (P < 0.01) in skeletal muscle from control subjects. However, the rate of insulin-stimulated 3-0-methylglucose transport was not altered in isolated skeletal muscle from the control subjects or the type 2 diabetic patients following exposure to 1.0 mmol/l oleate. This observation indicates that elevation of non-esterified fatty acids to a high physiological level has no inhibitory effect on glucose transport.