The application of a new, miniaturized portable digital data recorder "Thermoport" (Institute for Reproductive Medicine, Münster, West Germany) for continuous determination of scrotal temperatures revealed great variations of scrotal temperature during 24 hours in normal men. Maximum temperatures approached body core temperatures. Mean scrotal temperatures of 10 normal men rose during sauna from 32.72 +/- 0.23 degrees C to 37.53 +/- 0.38 degrees C. During treadmill running, scrotal temperatures increased by more than 2.5 degrees C. Minimal scrotal temperatures were increased in some men with varicocele compared with normal fertile men indicating impaired cooling mechanisms. The continuous temperature measurements facilitate assessment of temperature dynamics. The miniaturized design of the Thermoport makes it suitable for routine use in outpatients of infertility clinics, in occupational medicine for evaluation of heat hazards, and for investigations of body temperatures under various experimental conditions.