I have said that it is okay to mix breastmilk with formula, if there wasn't enough expressed breastmilk to use with the lactation aid. I believed that breastmilk enhanced the formula in that it helped to digest it. A client, who has a healthy 5 month old read in a Consumer's Report one should not mix the two. She also read in the same report that freezing affects the folate content of the breastmilk. I suggested that she should not worry at all, because she is mainly breastfeeding and pumping milk for when she returns to work next month. Marsha Walker's hand outs for premature infants listed a study by Quan, R., Clin Pediatr 1994; June 325-328. "Bacterial growth inhibition by breast milk was reduced by cow's milk based formulas". What is your practice, especially when the baby is not a healthy, full term infant? (not in this client's case) My question about the folate: Is it the freezing or the reheating (pasteurization) or both that affects the folate content? and in what situation would it really have an impact? Thanks for your thoughts. Kathy Bodden, IBCLC, Toronto