Five patients were admitted to our hospital because of classical heat stroke during the heat waves which attacked our country in the summers 1994 and 1995. The clinical and laboratory findings of all patients suggested the rapid progress of multiple organ dysfunction syndrome (MODS). Blood purification (BP) therapy, in addition to conventional treatment, was performed in three of the patients. Despite their disastrous general condition, all completely recovered or recovered sufficiently to be transferred to a rehabilitation hospital. Two additional patients were treated with conventional treatment only and both died in 1-3 days after admission. Clinical characteristics and laboratory findings on admission showed no differences between the cases receiving BP therapy and those not receiving BP therapy. These findings suggest that, in heat stroke patients, additional BP therapy may provide a better prognosis than conventional therapy only. These beneficial effects of BP may have been due mainly to the removal of proinflammatory cytokines related to heat stroke.