Slices of beef longissimus and gluteus medius muscles were stored sealed for 24, 48, 72, and 96 hr in a pigment-oxidizing atmosphere of 1%O2/99%N2. Greater (P<0.05) metmyoglobin formation occurred with increased storage time and the gluteus medius was less (P<0.05) color-stable than longissimus. Following storage in the low-O2 atmosphere, muscle slices were held 24 hr under aerobic conditions to allow pigment reduction. Absolute pigment reduction was greater (P<0.05) in slices stored 72 and 96 hr than in those stored 24 and 48 hr. Relative reduction was maximal at 72 hr. Differences in color stability between longissimus and gluteus medius muscles do not appear to be due to aerobic pigment reduction.