The substitution of sucrose for starch in the normal diets of young male volunteers induced a rise in the concentrations of cholesterol, triglycerides and phospholipids in the plasma. The rise in cholesterol was confined to the esterified fraction. Small random changes in energy intake resulting from the modification of the diets did not influence the results. A large increase in energy intake, by between 60 and 70%, promoted a substantial increase in the plasma cholesterol and triglycerides when sucrose consumption was simultaneously raised, but not otherwise. The large increase in fat intake during the period of over-eating had no effect on plasma lipids.