Levels of plasma vitamin K1 (VK1) and vitamin K2 (VK2) and protein-induced vitamin K absence-II (PIVKA-II) were measured in Japanese mothers and their newborn (N = 33). Twenty milligrams of VK1 (N = 11) or VK2 (N = 12) were given orally to randomly selected mothers 7 to 10 days prior to delivery. Means of plasma VK1 and VK2 concentrations were significantly higher in VK1 (p less than 0.01) and VK2 (p less than 0.01) treated mothers than in the controls at delivery, respectively. Similarly, these levels were significantly elevated in cord plasma in VK1 (p less than 0.05) and VK2 (p less than 0.05) treated groups, compared with findings in the control group, although there was a large concentration gradient between maternal and cord plasma (mostly less than one-tenth). A significant positive correlation was found in VK1 concentration between maternal and cord plasma (N = 33, p less than 0.01), and the proportion of PIVKA-II-positive infants was significantly lower in the VK treated groups than in the control group at birth (p less than 0.05). On the fifth postnatal day, mean levels of VK1 (p less than 0.01) and VK2 (p less than 0.01) in breast milk were significantly higher in the VK1 and VK2 treated mothers than in the control mothers, respectively. In the control group, 9 of 10 infants had a positive PIVKA-II, but no one in the treated groups was positive, thereby indicating significant differences between control and treated groups (p less than 0.01 and p less than 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)