Dantrolene (2.45 mg/kg body weight, range 2 to 4) was administered iv in eight heat stroke (HS) patients and compared with a control group of 12 patients of similar age, weight, and temperature range (41.9 degrees to 44 degrees C). Body surface cooling was conducted in air conditioned rooms at temperatures of 18 degrees to 23 degrees C. Mean cooling time in the dantrolene group was 49.7 +/- 4.4 (SEM) min, whereas cooling time in the control group was 69.2 +/- 4.8 min. The decrease in temperature was significantly greater in the dantrolene group, for whom the cooling time was decreased by about 19.5 min (p less than .01). Although cooling time was significantly shorter in the dantrolene group, there was no difference in the recovery of both groups. Dantrolene is an expensive drug and justification for its routine use in HS remains to be evaluated.