Muscle specimens from the quadriceps femoris muscle were obtained from eight healthy subjects by means of an open muscle biopsy and prepared for in vitro incubation. C-peptide at 0.5, 1.0 and 2.5 nmol/l increased 3-0-methylglucose transport by 38% (NS), 64% (p less than 0.05), and 64% (p less than 0.05) respectively. Glucose transport increased 1.8-fold in the presence of 0.3 nmol/l of insulin (p less than 0.05). Glycogen content in muscle strips exposed to C-peptide at a concentration of 1 nmol/l increased significantly by 22% (p less than 0.05). In conclusion, C-peptide stimulates the rate of 3-0-methylglucose transport in in vitro incubated human skeletal muscle strips in a dose-response manner. These observations suggest that C-peptide may contribute to the regulation of carbohydrate metabolism in human skeletal muscle.