One hundred and eighteen male rats (Long-Evans) were acclimated to experimental procedures (i.e., handling, transferring from and back to "home" cage, body weight and colonic temperature determinations) for 2 wk and then subjected to cage confinement for 3 days before microwave (MW) exposure to 2,450 MHz for 1-, h, at 1-70 mW.cm-2 or sham exposure at ambient temperature of 24 +/- 1 degree C. Colonic temperature increased after exposure to power densities greater than or equal to 20 mW.cm-2 and was the most sensitive parameter measured. Inverse relationships between corticosterone and thyrotropin or growth hormone were noted after exposure for 1 h at 50 mW.cm-2 and above. Pituitary-thyroid function was inhibited after exposure to 20 mW.cm-2 for 2-8 h. Changes in other hormones were transient or inconsistent. Corticosterone, thyrotropin, and growth hormone levels could be correlated with power density or colonic temperature in rats exposed to MW for 1 h; corticosterone and thyrotropin levles correlated with colonic temperatures in shams. Body temperature influences adenohypophysial hormones in studies of MW biological effects.