The iron status of nine female marathon runners was evaluated during 11 weeks of training for a marathon race and following a marathon race. Venous blood samples were obtained at the start of the training period, weekly during training, and 1, 2, 3, and 4 days post-race. The subjects completed menstrual and dietary histories, and the diet content of energy, protein, iron, and ascorbic acid was calculated. Serum iron, total iron binding capacity, and transferrin saturation showed no significant change at weeks 1, 7, and 11 during training. The mean values of serum iron and transferrin saturation were low. During training, eight of the nine women averaged serum ferritin levels below 50 ng/ml, one of the eight having values consistently less than 10 ng/ml. Ferritin values were significantly elevated for 3 days after the marathon. No subject reported abnormally heavy menstrual bleeding, and nutrient intakes were near recommended levels, except for iron. Thus, the iron status of these women marathon runners was poor, suggesting that women runners may have higher dietary needs for iron than sedentary women. Serum ferritin levels were also elevated after a marathon run and may not adequately reflect iron stores.