Iron deficiency in active men is well documented. To assess the relative importance of dietary iron intake, iron absorption, and iron loss in the pathogenesis of this iron deficiency, we compared a group of iron-deficient athletes to a group with normal iron stores. Iron absorption was assessed by an iron tolerance test. Serum haptoglobin was used as a measure of hemolysis. The presence of hemoglobinuria reflected urinary iron loss. Iron intake was determined by a 3-day dietary record as well as a food frequency questionnaire. Results showed iron absorption to be inversely correlated with iron stores. Iron-deficient athletes had higher absorption, suggesting a normal regulation mechanism. Major hemolysis (serum haptoglobin below 40 mg/dl) was found in 28% of subjects with no relationship to iron stores. No hemoglobinuria was detected after a usual training session. Iron intake was elevated in relation to high caloric intake, but iron intake in the form of meat was lower in iron-deficient athletes, as compared to those with normal or repleted iron stores. It is our opinion that inadequate iron intake is an important determinant of iron deficiency in athletes.