This study examined the effects of estrogen supplementation on markers of neutrophil infiltration and damage in skeletal muscle of rats following ischemia. Male and female gonad-intact rats, with or without 14 days of estrogen supplementation were subjected to two hours of hind-limb ischemia and sacrificed at 24, 48 or 72 hours post-ischemia. Control animals were sacrificed without ischemia. Plantaris and red and white gastrocneimus muscles were removed and assayed for myeloperoxidase (MPO), a marker of neutrophil infiltration, and glucose-6-phosphate dehydrogenase (G6PD) and ß-glucuronidase (<img border=0 width=8 height=15 id="_x0000_i1026" src="http://fbpe/img/bres/v38n2-3/existe.gif" align=absbottom>GLU), as markers of muscle damage. Significant elevations of MPO, G6PD and <img border=0 width=8 height=15 id="_x0000_i1027" src="http://fbpe/img/bres/v38n2-3/existe.gif" align=absbottom>GLU activities were observed at various time points post-ischemia. No systematic differences between genders were noted in any of the measures. Estrogen supplementation in both male and female animals failed to significantly attenuate post-ischemia increases in MPO, G6PD and <img border=0 width=8 height=15 id="_x0000_i1028" src="http://fbpe/img/bres/v38n2-3/existe.gif" align=absbottom>GLU activities in any of the muscles studied and in some cases accentuated activities of some of these measures. Unlike previous findings following exercise in skeletal muscle, this study failed to demonstrate estrogen-induced attenuation of indices of neutrophil infiltration or damage in skeletal muscles of rats up to 72 hours following ischemia. This demonstrates that estrogen may not consistently attenuate neutrophil infiltration and that a number of variables including damage modality, tissue or estrogen level may influence this.