To determine the effects of depleted iron stores on endurance performance and blood lactate concentration, eight active women with normal (>26 ng/ml) and eight with low (< I2 nglml) plasma ferritin concentrations were studied while performing a and an endurance test (80% ) on a cycle ergometer. The low femtin group had significantly lower serum iron concentration and transferrin saturation and higher TIBC than the normal femtin group. Mean was not significantly different between groups. No significant difference was found in total time to exhaustion during the endurance test for low (23.2 min) and normal (27.0 min) femtin groups; however, the normal femtin group exercised 14% longer. Blood lactate concentrations following the VOzmax and endurance test did not differ significantly between groups. Food diaries revealed lower daily absorbable iron intake by the low femtin group compared to the normal ferritin group. Ferritin concentration was significantly related to absorbable iron (r=.72) and total iron (r=.70) intake. The results suggest that women with depleted iron stores who are not anemic may have less endurance, but do not have higher blood lactate during exercise than women with normal iron stores.