Acute infections may influence the hemodynamic alterations of liver disease. Therefore, the hemodynamic effects of endotoxin (LPS E. coli 0111:B4) in conscious, normal, and cirrhotic rats were compared. Endotoxin decreased cardiac index in cirrhotic but not in normal rats. Although the effect of endotoxin on portal tributary blood flow was minor in all animals, a reduction in portal pressure was found in cirrhotic rats. Because the most marked hemodynamic effects were observed in cirrhotic rats, the second part of our study investigated whether platelet activating factor played a role in endotoxin-induced hemodynamic alterations in the cirrhotic model. Platelet activating factor reduced cardiac index and kidney blood flow but did not influence portal tributary blood flow. Two antagonists to platelet activating factor reduced the adverse renal blood flow lowering effects of endotoxin in cirrhotic rats. Thus, it is suggested that the hemodynamic changes observed in cirrhosis may be aggravated during acute infections. Under this condition, antagonists to platelet activating factor may be of benefit in the prevention of hemodynamic complications induced by endotoxin.