The systemic inflammatory response syndrome (SIRS) is a major cause of morbidity and mortality, and is thought to be due to an over-amplification of an inflammatory response. The Toll-like receptor 4 ( TLR4 ) Asp-299-->Gly polymorphism has been shown to reduce lipopolysaccharide responsiveness. We examined whether this TLR4 polymorphism is associated with severity of SIRS. A trend was found between the minor allele and mortality in SIRS (odds ratio of 4.3; P =0.076), suggesting a role for TLR4 signalling in the severity of SIRS.