Risk for coronary heart disease is increased in adult Caucasians with high serum lipoprotein(a) [Lp(a)] concentration. In adults the concentration is mainly regulated by genetic factors. Our previous study suggests that breast milk has a beneficial effect on serum Lp(a) concentration in infants. Now we analyzed the influence of weaning by measuring serum Lp(a) and cholesterol in 414 infants at 7, 13, 24, and 36 mo of age. At 7 mo the infants received, in addition to solid food, only breast milk (n = 148), breast milk and formula (n = 74), or formula only (n = 191). Median (range) serum Lp(a) concentrations were then 25 (