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LaMANCA J. J. and E. M. HAYMES. Effects of iron repletion on VO2mx, endurance, and blood lactate in women. Med. Sci. Sports Exerc., Vol. 25, No. 12, pp. 1386–1392, 1993. To determine the effects of an 8-wk dietary iron supplementation (100 mg.d-1) on low plasma ferritin concentration (<20 ng.ml-1) and endurance, 20 active women (19–35 yr) were studied while performing a O2maxtest and an endurance test (80 O2max) on a cycle ergometer. Subjects were randomly placed in an iron supplement (IG) or a placebo group (PG) using a double-blind method. After treatment in the IG, ferritin levels were higher (22.5 ± 3.4 vs 14.3 ± 2.2 ng.ml-1; P< 0.05), Hb increased (12.8 ± 0.4 to 14.1 ± 0.2 g.dl-1; P< 0.05), and TIBC decreased (366.2 ± 24.8 to 293.8 ± 14.0 μg.dl-1; P< 0.05). Also after treatment the IG's O2maxwas significantly greater (P<0.05) than the PG value and their postendurance blood lactate decreased (5.03 ± 0.44 to 3.85 ± 0.6 mM.1-1; P< 0.05). Endurance time to exhaustion increased 38 (37.28 ± 5.03 to 51.4 ± 7.45 min) following iron treatment; however, this change was not statistically significant. The results suggest that this level of iron supplementation can reverse mild anemia, increase O2max, and reduce blood lactate concentration after submaximal exercise.