Ten healthy male volunteers were exposed to the dry heat of a Finnish sauna (+ 80 oC) for 1 h twice a day for a period of 7 days. After each exposure rectal temperature rose by 0.8-1.1 oC and body weight dropped by 0.7-0.9 kg. The systolic blood pressure recorded 35 min after the sauna did not change during the experiments but the diastolic blood pressure decreased by 737 mmHg (P < 0.05). The pulse rate rose from 7580 to 106116 beats min-1 (P < 0.05) after the sauna. The increased responses of pulse and temperature adapted to heat exposures so that they were significantly lower after the 3rd day (rectal temperature) or after 6th day (pulse). Metabolic rate increased by 2533% (P < 0.01) after the first day. Serum total proteins, Hb and Htc were significantly increased on the 1st and 3rd days but not later, although the dehydration in response to sauna was unchanged as judged from the weight losses. Serum K, Na and Fe were significantly decreased on the 3rd and 7th day indicating that special attention should be given to the electrolyte balance in long-lasting intense heat exposure. No ECG changes were found in recordings taken on the 7th day.