Young male Sprague-Dawley rats were randomly assigned to one of three groups (Chronically Hypoxic, N = 15; Age-Control, N = 15; Weight-Control, N = 15) and studied immediately following a 36-day exposure at a simulated altitude of 5846m or after recovery periods of one, three or seven days. Following preincubation at pH 3.8, cross-sections of soleus muscle were stained by the calcium ATPase method and analyzed for six indices of skeletal muscle capillarity: capillary density (CD), fiber density, number of capillaries around each fiber (CAF), Capillary/fiber ratio (C:F), fiber cross-sectional area (FCSA), and fiber diameter. No differences in skeletal muscle capillarity were observed in chronically hypoxic rats at the termination of exposure or during the seven day recovery period. The Chronically Hypoxics differed significantly (p less than or equal to .05) from both control groups in three different measures of physiologic stress, but showed a definite trend toward recovery in the post-exposure period. This recovery was most apparent in body weight comparisons. The Chronically Hypoxics weighed less than the Age-Controls immediately following the exposure period but gained rapidly during the first three days post-exposure. These rapid body weight increases in rats recovering from chronic exposure to hypoxia suggest that age-controls should not be excluded in favor of weight-controls in similar studies.