The breastfed infant has limited sources of vitamin K, as it is transmitted poorly across the placenta and is present in very low concentrations in human milk. The author of this paper reports a concentration of vitamin K in human milk (0.517 +/- 1.521 microg/dl) that is about twice the average of earlier reports (0.25 microg/dl). About half of the increased concentration (0.235 +/- 0.144 microg/dl) is accounted for by vitamin K2 (menaquinone) rather than vitamin K1 (phylloquinone); the latter generally thought to be more important in human nutrition. The significance of these findings is discussed.