Urgent exposure to hyperbaric oxygen (HBO) is currently accepted as an effective therapy for cerebral air embolism. The diagnosis of air embolism in the critically ill post-surgical patient is frequently difficult and therefore the initiation of specific therapy is often delayed. Only limited information is currently available on the effects of delayed HBO treatment in these patients. We recently used HBO to treat five patients with cerebral air embolism resulting from invasive medical procedures; hyperbaric treatment was begun 15-60 h after the embolic event. The causes of air embolism were: cardiopulmonary bypass accidents, pulmonary barotrauma induced by mechanical ventilation, and central vein catheterization. All patients received initial treatment according to U.S. Navy Compression Table 6A in a multiplace chamber, followed by subsequent treatments with 100% O2 at 2.5 to 2.8 ATA for 90 min as indicated. Significant, partial or complete recovery was observed in three patients, one patient did not respond, and one died. The salutary effects of HBO in our subgroup of patients suggest that this treatment should be used in cerebral air embolism even when referral to a hyperbaric facility is delayed.