Dexamethasone (1 mg/kg, i.p.) administered either 1 hr before or 1 hr after E. coli lipopolysaccharide (LPS, 4 mg/kg, i.p.) in conscious rats inhibited the subsequent (4 hrs) rise in plasma cytokine (interleukin [IL]-1β, tumour necrosis factor [TNF]-α), nitrate/nitrite (NO×), soluble intercellular adhesion molecule-1 (sICAM-1) concentration and lung/liver myeloperoxidase activity indicative of an anti-inflammatory effect. Dexamethasone also reduced the LPS-evoked rise in plasma hydrogen sulphide (H2S) concentration, liver H2S synthesizing activity and expression of cystathionine γ lyase (CSE) and inducible nitric oxide synthase (iNOS). Mifepristone (RU-486) inhibited these effects. Dexamethasone (1–10 μM) reduced the LPS-evoked release of IL-1β, TNF-α and L-selectin, decreased expression of CSE and iNOS and diminished nuclear factor κB (NF-κB)-DNA binding in isolated rat neutrophils. In contrast, NaHS (100 μM) increased L-selectin release from rat neutrophils. Dexamethasone also reduced LPS-induced up-regulation of CSE in foetal liver cells. 6-amino-4-(4-phenoxyphenylethylamino) quinazoline (QNZ, 10 nM), a selective inhibitor of transcription via the NF-κB pathway, abolished LPS-induced up-regulation of CSE expression. We propose that inhibition of CSE expression and reduction in formation of the pro-inflammatory component of H2S activity contributes to the anti-inflammatory effect of dexamethasone in endotoxic shock. Whether H2S plays a part in the anti-inflammatory effect of this steroid in other forms of inflammation such as arthritis or asthma warrants further study.