To determine the risk of sauna bathing after heavy exercise, the responses of 10 clinically normal adult males (mean age 45 years) were observed and recorded for 26 min during recovery from a standard, heavy exercise task on 2 separate days. On one of the 2nd days, recovery was interrupted by a 10 min (min 6-16) exposure to intense, dry heat (70-74.degree. C, 3-6% relative humidity). The higher heart rate and rectal temperature during the treatment (min 6-16) and post treatment (min 16-26) phases on the experimental day were indicative of the expected response to the heat stress. Systolic blood pressure did not differ on experimental and control days during either phase of recovery. Diastolic blood pressure decreased during the heat exposure. Double product was higher during treatment and posttreatment phases on the experimental day indicating an increased myocardial O2 need in response to the heat. ECG changes were limited to increased J-point displacement during the treatment phase on the experimental day, with S-T segment flattening (0.08 s) in 1 case, and prolongation of the Q-T interval (corrected for rate) with reduction in T-wave amplitude. The prolongation of electrical systole and T-wave flattening were not observed during exercise at comparable and higher heart rates and may be associated with reduced subendocardial perfusion. Sauna bathing of short duration after exercise apparently represents a tenable risk for clinically normal males.