Peripheral vascular structure was studied using measures of forearm blood flow and forearm vascular resistance. Measurements of peripheral vascular structure were compared to data on sodium sensitivity and potassium sensitivity in the population. Insulin resistance was studied using the euglycemic hyperinsulinemic clamp technique. Variations in the activity of the sodium-potassium pump and sodium-hydrogen exchange in red cells were correlated with insulin resistance to determine if hyperinsulinemia alters cation transport rates.