The clinical picture and the final outcome of 30 patients with heat stroke during the Mekkah pilgrimage 1404 (September 1984) were analysed. Rapid cooling by the 'evaporative method' was achieved in a mean time of 59 min (range 15-135). An initial temperature above 42 degrees C and a cooling time of more than 1 h indicated a poor prognosis. Acute hepatic failure, 'adult respiratory distress syndrome' and decerebrate convulsions were among the fatal complications occurring in three patients. In the final outcome three patients (10 per cent) died, two patients (7 per cent) recovered but developed myocardial infarction and cerebellar ataxia respectively. Twenty-five patients (83 per cent) made an uncomplicated recovery.