Hepatic complications are common in patients receiving total parental nutrition (TPN) and who have no underlying liver disease. In the present study we examined the hypothesis that endotoxin (LPS) or possibly TNF derived from the overgrowth of intestinal gram-negative bacteria is responsible for TPN-associated hepatic steatosis, and that bowel decontamination and specific anti-LPS activity of polymyxin B will reduce fatty infiltration of the liver during TPN. Forty-five male Sabra rats underwent jugular vein cannulation, were placed in metabolic cages, and were randomized into five groups. Group I was continuously infused with normal saline and allowed food ad lib, while group II-V were continuously infused with a TPN formula containing 4.25% amino acids and 25% dextrose for a total of 36 calories and 3.0 g protein per 100 g body weight/day. In addition, groups III-IV were also treated by oral polymyxin B while Groups IV and V received a combination of neomycin, metronidazole, and vancomycin (NMV). Thus, Group III received polymyxin B, Group IV received both polymyxin B and NMV, while Group V received NMV only. On Days 7-8 of the study, all animals were sacrificed and spontaneous production of TNF by peritoneal macrophages, bacterial translocation to mesenteric lymph nodes, culture of the cecum, and fat, triglyceride, and cholesterol contents of the liver were determined. All groups infused with TPN exhibited higher levels of total fat, triglycerides, and cholesterol compared to the free feeding control group (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)