Low vitamin K-1 intakes have been associated with low bone mineral density in women and reduced bone turnover in girls. No European data exist on the relationship between vitamin K-1 and serum undercarboxylated osteocalcin (ucOC), an indicator of K-1 status in adolescents. The aim of the current study was to assess intakes of vitamin K-1 in relation to serum ucOC status in Irish girls. A detailed deietary history method, which measured habitual intakes from a typical 14-day period, was used to estimate vitamin K-1 intakes in 18 girls aged 11-13 years. Recently compiled and validated food composition data for vitamin K-1 were used to determine vitamin K-1 intakes. An enzyme immunoassay was used to measure ucOC in fasting serum samples. The mean (+/- SD) intake of vitamin K-1 in the girls was 72.4 mu g/day (SD 34.4). Vegetables (particularly broccoli, composite dishes, and lettuce) contributed 53% of total vitamin K-1 intakes. Thirty-Seven percent of the girls failed to meet the current U.S. adequate intake for adolescents of 60 mu g/day vitamin K-1. Serum ucOC levels were inversely related to body weight-adjusted vitamin K-1 intakes, controlling for energy intake (partial correlation r = -0.538; p = 0.026). The data indicate that large-scale studies to examine relationships between vitamin K-1 (and green vegetable) intakes and bone growth and development in adolescents are warranted.