One- and two-hour postprandial glucose and insulin values were measured in 58 submariners with 5 or more FBM patrols and in 58 non-submariners. An interrelationship between serum glucose and insulin for classifying defects in carbohydrate metabolism indicated that 55% of the submariners and 45% of the non-submariners exhibited some type of defect. Exercise appears to play an important role in the maintenance of normal carbohydrate metabolism in these subjects. Non-submariners reported engaging in significantly more exercise than did submariners. Negative correlation between exercise vs. 1 and 2-h glucose and 2-h insulin was significant for all subjects. An inverse relationship was observed between amount of exercise and the severity of carbohydrate metabolic defects in submariners and non-submariners as well as in normal weight and obese individuals. No statistical differences were found between the submariner and non-submariner groups with respect to age, % body fat, fatness (normal or obese), glycosylated hemoglobin, or family history of diabetes.