Injection of bacterial lipopolysaccharide (LPS) into animals results in a transient increase in serum tumor necrosis factor (TNF). Maximal increases in TNF were detected by 1 h and 3-4 h serum TNF was no longer apparent. These animals were LPS tolerant and a repetitive LPS stimulus did not result in an additional peak in TNF. Regulation of TNF expression in LPS-tolerant animals was at the transcriptional level as TNF mRNA was not apparent in spleen or peritoneal macrophages following a second LPS stimulus. Adrenalectomized (adrex) mice, in contrast, did not become LPS tolerant and sera from these animals demonstrated an additional peak in TNF 1 h following a second LPS stimulus. Concomitant with the secondary rise in serum TNF in adrex mice was an increase in splenic TNF mRNA. The ability of adrex mice to become LPS tolerant was restored by exogenous glucocorticoids. LPS tolerance was also investigated in the galactosamine LPS model which like the adrex model is characterized by a thousandfold increase in the sensitivity of these animals to the lethal effects of LPS. Consistent with the absence of LPS tolerance in adrex mice, galactosamine-sensitized mice were also responsive to a second LPS stimulus and did not become LPS tolerant. While LPS-treated adrex mice had no significant increases in serum corticosterone, corticosterone levels in LPS-treated galactosamine-sensitized mice were comparable to LPS-stimulated normals suggesting that LPS tolerance involves both glucocorticoid-dependent and -independent components. Finally, prophylactic administration of a monoclonal antibody against murine TNF protected normal and galactosamine-sensitized mice from a lethal dose of LPS and yet had no protective effect in adrex animals.