The effects of environmental air temperature of 6 degrees C and 26 degrees C on catecholamines (CA) and circulation were studied in eight male subjects during rest and during bicycle exercise at WOBLA for 45 min each. We found that resting at 6 degrees C increased the norepinephrine (NE) levels to the same levels as endurance exercises at 6 degrees C. The increase of CA levels was 2.5 to 3 times higher during work at 26 degrees C compared with 6 degrees C. During both rest and exercise at 6 degrees C we found a higher stroke volume of the heart and a reduced heart rate (HR) with no or only small effects on the oxygen uptake and blood lactate levels compared with 26 degrees C. Measurements of the skin temperatures showed large differences both at rest and during work; those of core temperature showed no changes at rest and a slightly more pronounced increase during work at 26 degrees C compared with 6 degrees C. The behavior of CA, plasma renin activity (PRA), plasma aldosterone (PA), and circulation were studied in 13 top class swimmers and 12 recreational swimmers during immersion into water of 27 degrees C for 10 min. The recreational swimmers were additionally immersed into water of 21 degrees C and 33 degrees C. Even immersion at 33 degrees C induced a small but significant increase of NE levels and of blood pressure (BP) values with no effect on the HR and blood lactate values. Epinephrine (EPI) showed a tendency to decrease.(ABSTRACT TRUNCATED AT 250 WORDS)