We investigated the influence of altered glucose levels on insulin-stimulated 3-0-methylglucose transport in isolated skeletal muscle obtained from NIDDM patients (n=13) and non-diabetic subjects (n=23). Whole body insulin sensitivity was 71% lower in the NIDDM patients compared to the non-diabetic subjects (p <0.05), whereas, insulin-mediated peripheral glucose utilization in the NIDDM patients under hyperglycaemic conditions was comparable to that of the non-diabetic subjects at euglycaemia. Following a 30-min in vitro exposure to 4 mmol/l glucose, insulin-stimulated 3-0-methylglucose transport (600 pmol/l insulin) was 40% lower in isolated skeletal muscle strips from the NIDDM patients when compared to muscle strips from the non-diabetic subjects. The impaired capacity for insulin-stimulated 3-0-methylglucose transport in the NIDDM skeletal muscle was normalized following prolonged (2 h) exposure to 4 mmol/l, but not to 8 mmol/l glucose. Insulin-stimulated 3-0-methylglucose transport in the NIDDM skeletal muscle exposed to 8 mmol/l glucose was similar to that of the non-diabetic muscle exposed to 5 mmol/l glucose, but was decreased by 43% (p <0.01) when compared to non-diabetic muscle exposed to 8 mmol/l glucose. Despite the impaired insulin-stimulated 3-0-methylglucose transport capacity demonstrated by skeletal muscle from the NIDDM patients, skeletal muscle glycogen content was similar to that of the non-diabetic subjects. Kinetic studies revel a Km for 3-0-methylglucose transport of 9.7 and 8.8 mmol/l glucose for basal and insulin-stimulated conditions, respectively. In conclusion, the impaired capacity for insulinstimulated glucose transport in skeletal muscle from patients with NIDDM appears to protect the cell from excessive glucose uptake under hyperglycaemic conditions. Furthermore, the in vitro normalization of the decreased insulin-stimulated glucose transport in NIDDM skeletal muscle following exposure to 4 mmol/l glucose suggests that glycaemia per se has a profound effect on the regulation of muscular glucose transport.