A secondary reference regarding the effect of free iron in formula in the mostly breastfed baby's gut is: Pryor, Karen and Pryor, Gale. "Nursing Your Baby" 1991, Chapter 3, page 79. " The high bioavailability of iron in human milk disappears, however, when supplemental feedings are added. The breastfed baby who is getting bottles of artifical milk as well should have additional iron in the diet." The bibliography for chapter 3 is extensive but not specifically footnoted. I *think* the primary reference which she is citing is Goldman, A.S., C. Garza et al1990. Molecular forms of lactoferrin in stool and urine from infants fed human milk. Ped. Res. 27(3):252-55. This is a fantastic book and I think Chapter 3 ought to be required reading for every woman and doctor on the planet. If Karen and/or Gale Pryor are on Lactnet please issue a 3rd updated edition! Cindy N.