This study was designed to assess the effects of hypohydration (-5% body weight) and heat acclimation on plasma cortisol (PC) and growth hormone (GH) responses to exercise (1.34 m X s-1) in a hot-wet (35 degrees C, 79% rh) or hot-dry (49 degrees C, 20% rh) environment. Preacclimation, hypohydration in both the hot-wet and hot-dry environments resulted in significant (p less than 0.05) increments in PC levels during the fourth exercise interval. Acclimation had no effects on PC levels in the euhydrated condition, but in the hot-wet environment there did occur an attenuation of the PC response when hypohydrated. Preacclimation exercise in either the hot-wet or hot-dry environment resulted in significant (p less than 0.05) increments in GH when euhydrated. While the effects of acclimation were inconsistent, hypohydration generally resulted in elevated levels of GH compared to euhydration. We concluded from these studies that hypohydration to -5% of body weight generally elicited elevations in circulating levels of stress hormones, and that acclimation did not effect consistent decrements in these responses.