In 44 very low-birth-weight infants, fecal cholesterol excretion was measured and in 29 other infants serum total cholesterol concentrations in response to different cholesterol intakes were studied. The infants received fortified breast milk (mean cholesterol content 15.3 mg/dl) or were fed either a standard preterm formula (cholesterol content 5.5 mg/dl) or the same formula but with a modified lipid composition (long chain polyunsaturated fatty acid concentration closely related to breast milk fat) and 30 mg of cholesterol/dl. In the group fed the high cholesterol formula, fecal cholesterol excretion was significantly higher (35.5 mmol/kg/day) than in the groups fed breast milk or the standard formula (20.1 and 18.2 mmol/kg/day). Cholesterol balance in the group fed the high cholesterol formula (21.8 mg/kg/day) was significantly higher than in the group fed breast milk (+8.6 mg/kg/day). In the infants fed the low cholesterol formula the balance was negative (-7.7 mg/kg/day). Serum concentrations of total cholesterol were similar in the groups fed breast milk or the high cholesterol formula (3.47 and 3.51 mmol/l), but significantly higher than in the group fed the low cholesterol formula (3.15 mmol/l). The data suggest that preterm infants are able to regulate a higher cholesterol intake than during breast feeding by increasing fecal cholesterol excretion as well as decreasing endogenous synthesis.