In fulminant liver failure (FLF) there is need for support as a bridge to liver transplantation. Based on the concepts of hemofiltration and xenotransplantation, the authors present a model of liver support in FLF. The authors performed a portacaval shunt and ligature of the hepatic artery in 12 pigs. In six pigs (Group A) continuous hemofiltration through a polyacrylonitrile membrane was performed. Six isolated dog's livers were catheterized through the portal vein and perfused with autologous erythrocytes, albumin, and electrolytes in a closed circuit. With the use of the auxiliary liver, the circuit was connected to one of the lateral outlets of the hemofilter, while the other lateral outlet was connected to the portal vein through the pump. Thus, a polyacrylonitrile exchange membrane was created between the blood of the pig with FLF and the auxiliary liver's circulation. In Group B (controls), six pigs were connected directly to the auxiliary liver through a pump. In Group A, the auxiliary liver worked for 8 hr, without evidence of macroscopic or histologic damage. Lactic acid and ammonia levels improved: lactic acid, 8.2 +/- 6 mmol/L to 1.6 +/- 1 mmol/L; ammonia 487 +/- 110 micrograms/dl to 117 +/- 13 micrograms/dl, p < 0.1. The lidocaine clearing (MEGX) test results remained at functional levels (> 90 ng/ml) at the end of the perfusion. In Group B, the perfusion was discontinued at 60 +/- 15 min because of evidence of necrosis of the auxiliary liver. Lactic acid levels increased from 8.19 +/- 1.1 mmol/L to 13 +/- 4 mmol/L, ammonia levels remained high (390 +/- 15 micrograms/dl to 480 +/- 80 micrograms/dl), and the MEGX test results showed levels below functional activity by the end of the perfusion (45 +/- 30 ng/ml). The authors conclude that the concept of xenohemodiafiltration based on the interposition of a polyacrylonitrile membrane between a xenograft and an animal in FLF is adequate to support functions of detoxification and could be used in the future in the support of patient with FLF.