Modalities of oxygen therapy for pregnant women intoxicated with carbon monoxide (CO) are ill defined. Hyperbaric oxygen (HBO) is presumed to be hazardous to the pregnancy. On the other hand CO entails anoxic injuries in the mother and fetus. We have entered 44 pregnant women who sustained an acute carbon monoxide poisoning at home, into a prospective study in order to assess HBO tolerance. They were treated within 5.3 +/- 3.7 h (range: 1-12) of the intoxication with a combination of 2 h of HBO at a pressure of 2 atmospheres absolute (ATA) and 4 h of normobaric oxygen, irrespective of the clinical severity of the intoxication and of the age of pregnancy. Six patients were lost to obstetric follow-up. Only 2 patients sustained a spontaneous abortion: 1 within 12 h and 1 within 15 days of the intoxication. Thirty-four women gave birth to normal newborns. Finally 1 elected to undergo abortion for reasons unrelated to the intoxication and 1 gave birth to a baby with Down's syndrome. There is no evidence that HBO was involved with either abortion of our study. We conclude that HBO may be carried out in pregnant women acutely intoxicated with carbon monoxide.