Tympanic (Tty), esophageal (Tes), forehead, and hand skin temperatures, as well as the forehead evaporation rate were recorded in six men (four suffering from rosacea and two healthy controls) before, during, and after 1 h of warm bath (38 degrees-39 degrees C). During the last 30 min of the bath, the subject's face was vigorously fanned (14 m/s). Blood flow was explored with ultrasonic Doppler in the emissary veins of the cranium during normothermia before entering the bath, and during hyperthermia just after leaving it. Under normothermic conditions, Tty was higher than Tes in all subjects. In three patients, no blood flow could be detected in the ophthalmic emissary veins whereas in the fourth patient as well as in both control subjects, blood flowed from the intracranium to the face. During hyperthermia, face fanning decreased Tty by 0.25 degrees +/- 0.05 degrees C (+/- SEM) below Tes in the control subjects whereas in all patients Tty remained warmer than Tes by 0.1 degrees C. Doppler recordings showed a rapid inward blood flow from the skin to the brain in the controls during hyperthermia. In patients, however, there was no change from normothermia in the blood flow patterns of vena angularis oculi. Their forehead temperature was permanently higher than in control subjects. Venous blood flow from the skin to the brain appears to be suppressed in rosacea, thus inhibiting selective brain cooling in hyperthermic conditions. The importance of this mechanism in the pathogenesis of rosacea and its significance as a means of investigation are discussed.