Twelve obese normotensive females were studied to determine the effects of either a 71% carbohydrate (HC) hypocaloric diet or a 33% carbohydrate (LC) hypocaloric diet concommitant with an aerobic exercise program on sodium (Na) balance and blood pressure changes. Subjects participated three times a week in a submaximal periodic exercise session and were placed on one of the diets for 28 days. Posttreatment, each participant consumed a 1000 kcal mixed diet while remaining in the exercise program. Daily Na losses were measured by 24 hr urine collection, and blood pressure measurements were made weekly. Both treatment groups significantly decreased in weight with LC losing more than HC (8.0 kg by LC group; 6.7 kg by HC group). Although urine Na balance was negative for the first 2 days of both VLCD's, Na excretion fell over time to result in net Na retention over the experimental period. Though the LC group lost more Na during the first week than EC during subsequent weeks, the differences between groups were nonsignificant. There were no significant differences between groups in serum Na or urine Na balance. However, Na urinary loss significantly decreased across time. Both systolic and diastolic blood pressure decreased non-significantly an average of 4% from baseline values throughout the treatment (5.2/4.0 mmHg in the HC group and 4.3/2.3 mmHg in the LC group). Carbohydrate inclusion in both diets was found to be effective in retaining Na after 4 days on a VLCD. Changes on different postural positions did not reveal evidence of hypotension. Overweight normotensive individuals did not reduce blood pressure values below normal levels. / M.S.