The hepatoprotective effect of prostacycline was studied after in vitro and in vivo CCl4 liver injury. It was found that PGI2 could partly restore the amino acid incorporation after in vitro CCl4 poisoning. In the in vivo system PGI2 was capable of decreasing the elevated SGOT levels and the accumulated triglyceride in the liver, and to increase hepatic glycogen content 24 hours after CCl4 injury.