The purpose of this study was to support the hypothesis that cytokines such as interleukin-1, tumor necrosis factor and interleukin-6 are released by macrophages or monocytes within 1 to 2 hr of phagocytosis of circulating, gut-derived backterial lipopolysaccharide translocated by acute liver injury. Time courses of fever, neutrophilia and low blood-zinc levels generally attributed to cytokines were quantified after partial (37%) hepatectomy of rats under ether anesthesia. These acute phase responses in hepatectomized rats were compared with those after intravenous injection of exogenous endotoxin and human natural interleukin-1. Fever commenced 30 min after interleukin-1 injection, 4 hr after exogenous lipopolysaccharide injection and 6 hr after 67% liver resection. Similarly, rectal temperatures were significantly elevated in recipient rats 30 min after intravenous administration of donor plasma from hepatectomized animals, indicating that cytokines, not lipopolysaccharide, elicited the febrile response. Neutrophilia was present 1, 2, and 4 hr after interleukin-1 injection, lipopolysaccharide injection and hepatectomy, respectively. Furthermore, the reduction in plasma zinc, which depends on cellular metallothionein synthesis, occurred 4 hr after interleukin-1 administration and 6 hr after lipopolysaccharide injection or partial hepatectomy. Donor plasma from hepatectomized rats also elicited neutrophilia at 1 hr and low blood-zinc levels 4 hr after injection in recipient animals. The timing of these responses, just as for the fever, implies that cytokines and not lipopolysaccharide in the donated plasma elicited the neutrophilia and hypozincemia. Evidence was reviewed that interleukin-1, tumor necrosis factor and interleukin-6 function as hepatotrophic factors and have been identified in the circulation of humans with liver damage. This complements the conclusion of this study that unspecified cytokines are released after partial hepatectomy of rats.(HEPATOLOGY 1990;11:923-931.).