The purpose of the present investigation was to determine whether female runners who consume a modified vegetarian diet are predisposed to iron deficiency. Two groups of female runners who were matched for age, weight, aerobic capacity, miles run per week, and number of pregnancies were obtained for this study. One group (N=9) regularly consumed a modified vegetarian diet (MV, <100 g red meat-wk-1), while the other group (N=9) consumed a diet which included red meat (RM). Serum ferritin values were significantly (P < 0.05) lower for the MV group (X ± SE, 7.4 ± 1.4 ng-100 ml-1) than for the RM group (19.8 ± 4.2 ng-100 ml-1). Total iron binding capacity (TIBC) of the serum was also significantly different between the two groups of subjects (MV, 366.5 ± 12.2 /xg-100 ml-1; RM, 327.2 ± 9.6 g. 100 ml-1). While dietary iron intake was comparable for the two groups (MV, 14.7 + 2.0 mg-d-1; RM, 14.0 ± 2.2 mg-d-1), the bioavailability of the dietary iron was significantly different (MV, 0.66 + 0.08 mgd-1; RM, 0.91 ±0.10 mg-d-1). As the presence of heme iron (from meat, fish, and poultry) increases the bioavailability of dietary iron, the results of the present investigation suggest that vegetarian athletes have altered iron status due to the form in which their dietary iron is consumed