We introduced a rapid rewarming technique as part of standard therapy in 16 newborn infants with effects of severe environmental hypothermia. On admission, mean rectal temperature was 31.0 +/- 2.7 degrees C, mean gestational age was 33.4 +/- 4.5 weeks, and mean birth weight was 1.76 +/- 0.71 kg. Thirteen infants were admitted within 30 hours of delivery, and the remainder at 2 to 3 weeks of age. Infants were rewarmed under a radiant warmer. The mean time required to reach a rectal temperature of 36.5 degrees C was 3.96 +/- 2.37 hours. Major medical entities encountered included thrombocytopenia (eight patients), metabolic acidosis (eight), respiratory distress (eight), renal failure (six), apnea (four), patent ductus arteriosus (four), seizures (four), intracranial hemorrhage (three), infection (three), and necrotizing enterocolitis (two). No complications could be attributed to the rapid rewarming technique. Of three infants who died, all weighed less than 1.25 kg at birth. This 81% survival is in contrast to the high mortality (25% to 50%) noted previously among infants treated by gradual rewarming.