B vitamin transport systems in infants are not as well studied as those for amino acids and glucose. For most B vitamins, a 2-step process allows for digestion of coenzyme forms of the vitamins in food, followed by specific transport systems for the free vitamin in the intestine. Folate and vitamin B12 have specific binding proteins, which carry the vitamins in human milk and blood, and other unique binding proteins, which convey the vitamins across the placenta, intestine, and blood-brain barrier. The permeable infant intestine permits the efficient intact transfer of protein-bound folate and vitamin B12 from intestinal lumen to bloodstream. As the intestine matures, specific carriers and receptors facilitate uptake and transport of these vitamins.