The present study compared the effects of several inhibitors of arachidonic acid metabolism on hypoxic pulmonary vasoconstriction (HPV) in Hilltop and Wistar rats. The results showed that HPV is much higher in Hilltop rats than in Wistar rats. U-60257B, an inhibitor of leukotrienes synthesis, resulted in a 46.7% reduction of HPV in Hilltop rats and 88.7% in Wistar rats. After an injection of U-63557A, an inhibitor of TXA_2 synthetase, HPV was reduced in Hilltop rats and was not changed in Wistar rats, so that the difference of HPV between these two strains of rats was eliminated. Indomethacin, inhibiting the synthesis of both PGI_2 and TXA_2, markedly enhanced the HPV in Wistar rats and diminished the HPV in Hilltop rats. It is suggested that roles of different prostaglandins may be the important factor in relation to the difference of HPV between Hilltop and Wistar rats.