The effects of Salmonella abortus equi lipopolysaccharides (LPS) on pure cultures of rat Kupffer cells (Kc) were studied. In vitro, LPS is ingested by Kc and located in vacuoles and secondary lysosomes. Culture of Kc in the presence of 1-50 micrograms LPS/ml during 24 h did not affect the viability of the Kc as measured by trypan blue exclusion, neutral red uptake, lactate dehydrogenase leakage and cell survival and spreading. LPS treatment did not influence the ultrastructure of Kc. The exposure of Kc to LPS in vitro did not change the phagocytic activity. Several biochemical processes were stimulated: glucose consumption, MTT-tetrazolium salt reduction, total protein synthesis and secretion of proteins. LPS activated Kc to tumoricidal activity against L929 mouse fibrosarcoma cells. In the light of the above observations, it is concluded that purified LPS is not cytotoxic for pure Kc in culture. On the contrary, LPS stimulates several biochemical and functional processes.