The effects of cold acclimation (CA) on the cardiorespiratory responses to cold air and water stress tests (CST) were studied in 7 males before and after a CA program of daily 90-min cold water (18 degrees C) immersions repeated 5 times a wk for 5 consecutive wk. The CST consisted of a 90-min resting exposure to cold air (5 degrees C, 30% relative humidity) or water (18 degrees C) during which rectal temperature, oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), heart rate, cardiac output (Q), and blood pressure (BP) were periodically measured. In cold air following CA, the VO2 at 10 min was lower (P less than 0.02) post- than pre-CA, however, no differences were found in cold water. The VE increased (P less than 0.01) during CST as a function of VCO2. The CA did not affect the VE-VCO2 relationship or the pattern of breathing during CST in cold air or water. The CA had no effect on Q or (a-v) O2 difference, which both increased (P less than 0.01) during the first 45 min of CST, then remained stable. BP increased significantly during the first cold water exposure, but not during the last cold water immersion. These data indicate that CA attenuated the onset of metabolic heat production during CST in air but did not alter its ultimate magnitude or the relationships between the cardiorespiratory variables and metabolic requirements. Also, the thermoregulatory adjustments associated with CA altered the control of blood pressure during acute cold stress.