The relationship between exercise and a high-calorie, high-saturated-fat diet was studied over a 22-week period in 101 Marine trainees with an average age of 20.5 yr. Their diet consisted of 4,500 calories (fat 2,025 calories or 225 gin, carbohydrates 2,025 calories or 506 gm, and proteins 450 calories or 112 gm). The program consisted of 16 hr of rigorous daily activity. There were no statistically significant changes in serum uric acid, lipid phosphorus, total cholesterol, lactic dehydrogenase, and malic dehydrogenase. Weight and blood pressure did not change. Serum content of triglycerides rose significantly, and isocitric dehydrogenase dropped significantly. It is suggested that a high-calorie and high-saturated-fat diet (milk, butter, and eggs) may not be atherosclerogenic if sufficient calories are utilized to offset this intake.