Eight healthy young men were studied during three periods of heat exposure in a Finnish sauna bath: at 80 degrees C dry bulb (80 D) and 100 degrees C dry bulb (100 D) temperatures until subjective discomfort, and in 80 degrees C dry heat, becoming humid (80 DH) until subjective exhaustion. Oral temperature increased 1.1 degrees C at 80 D, 1.9 degrees C at 100 D and 3.2 degrees C at 80 DH. Heart rate increased about 60% at 80 D, 90% at 100 D and 130% at 80 DH. Plasma noradrenaline increased about 100% at 80 D, 160% at 100 D and 310% at 80 DH. Adrenaline did not change. Plasma prolactin increased 2-fold at 80 D, 7-fold at 100 D and 10-fold at 80 DH. Blood concentrations of the beta-endorphin immunoreactivity at 100 D, adrenocorticotropic hormone (ACTH) at 100 D and 80 DH, growth hormone at 100 D and testosterone at 80 DH also increased, but cortisol at 80 D and 100 D decreased. The plasma prostaglandin E2 and serum thromboxane B2 levels did not change. Patterns related to heat exposure were observed for heart rate, plasma noradrenaline, ACTH and prolactin in the three study periods.