The effects of hot and cool environments on perceptual and physiological responses during steady-state exercise were examined in men (n = 14) performing 30 min of constant exercise (cycle ergometry) at a perceived exertion of "somewhat hard". Subjects exercised at the same absolute exercise intensity in hot (40 degrees C), neutral (24 degrees C), and cool (8 degrees C) conditions. Data were collected for differential ratings of perceived exertion (RPE), affect, thermal sensation, mean skin (Tsk) and rectal temperatures (Tre), and cardiac frequency (fc). The subjects completed the hot exposure with an average Tsk of 37.5 degrees C (SEM 0.11), while the neutral and cool conditions produced values of 33.8 (SEM 0.09) and 28.2 degrees C (SEM 0.30), respectively. The Tsk was significantly higher in the hot than the neutral and cool conditions throughout exercise (P < 0.05). The fc was significantly lower in the cool than in the other conditions (P < 0.05), and the subjects completed the hot exposure with a mean fc more than 20 beats.min-1 greater than observed in the other conditions. The subjects felt worse (lower affect) in the heat throughout exercise (P < 0.05). Overall RPE was significantly lower in the cool than in the heat, while chest RPE scores for the cool and hot conditions were displaced vertically by approximately two points. Subjects perceived work to be harder, felt worse, and experienced greater thermal sensation in the hot condition, compared with the neutral and cool conditions. Changes in cutaneous vasomotor tone and heat-induced influences on the chest may have accounted for the RPE changes observed in the heat.