We studied the duration of survival and the removal of putative toxins in forty pigs with ischaemic hepatic necrosis, undergoing haemodialysis or cross-dialysis with a large-pore membrane. Ischaemic hepatic necrosis was induced in conscious animals by tightening a loop around the hepatic artery 3 days after construction of a portocaval shunt. Pigs treated by a dialysis procedure survived significantly longer (45.2 +/- 11.9 h) than controls (26.3 +/- 5.4 h). There was no difference between haemodialysis and cross-dialysis. Blood ammonia initially dropped significantly (P less than 0.05) more during haemodialysis (560 +/- 107 leads to 210 +/- 51 mumol/l) than during cross-dialysis (596 +/- 131 leads to 398 +/- 81 mumol/l) but it subsequently increased beyond initial values despite efficient removal during continuous dialysis. Removal of ammonia was greater during cross-dialysis than during haemodialysis, but haemodialysis was more effective in the removal of the ammonia precursors glutamine and urea. We conclude that dialysis procedures can prolong survival in pigs with ischaemic hepatic necrosis. The removal of ammonia-precursors is more effective in the prevention of hyperammonaemia than the removal of ammonia itself. Since dialysis cannot prevent progressive hyperammonaemia, control of excessive toxin production seems mandatory for effective hepatic support.