Thirty three New Zealand rabbits were randomly divided into three groups, i.e. the control group, the high atmospheric pressure. (HAP) group and the hyperbaric oxygenation (HBO) group. The experimental animals were made into the models of reperfusion for acute incomplete cerebral ischemia. The blood-gas analyses drawn from the common carotid arteries and the internal jugular veins were carried out, and the 6-keto-PGF1a and TXB2 in the brain tissues determined. The results showed that the contents of 6-keto-PGF1a in the brain tissues of the HBO groups were significantly increased (P less than 0.01). While those of TXB2 were significantly decreased (P less than 0.01). The po2 in both the arterial and the venous blood were obviously elevated in the HBO group. Pathological examination showed that the brain tissue damages in the HBO group were the slightest among the three groups. It was postulated that the effect of HBO on 6-keto-PGF1a and TXB2 might reflect one of the mechanisms of HBO for the treatment of acute cerebral ischemia.