Forced-air warming is used for prevention or reversal of hypothermia in surgical patients. In the present study, the efficacy of this system for treatment of immersion hypothermia was evaluated. Six men and two women were twice immersed in 8 degrees C water until hypothermic. They were then rewarmed by either: 1) shivering-only inside a sleeping bag; or 2) forced-air warming. Esophageal and skin temperature, cutaneous heat flux and metabolism were measured. Afterdrop (+/- SD) during forced-air warming (0.43 +/- 0.26 degrees C) was approximately 30% less than during shivering (0.61 +/- 0.26 degrees C) (p < 0.001). Rewarming rate during forced-air warming (3.26 +/- 1.8 degrees C.h-1) was not significantly different from shivering (3.02 +/- 1.2 degrees C.h-1). Skin temperature was higher during forced-air warming by 3.7 degrees C early and 4.5 degrees C after 35 min of warming. Heat production increased by 77 W over the initial 20 min of shivering, and subsequently declined, compared to an immediate decrease with forced-air warming. During shivering heat flux ranged from 30 W early in rewarming, to 50 W after 35 min, compared to -237 W and -163 W respectively, for forced-air warming. Forced-air warming attenuated afterdrop and the metabolic stress of shivering while maintaining an average rate of rewarming comparable to shivering. Forced-air warming is a safe, simple, noninvasive treatment and could be used effectively in an emergency medical facility, and possibly in some rescue/emergency vehicles or marine vessels.