Tissue factor (TF), a small membrane bound high affinity receptor for factor VII, has an important procoagulant role in the haemostatic dysfunction associated with severe sepsis. Using an in vitro model of human endothelial TF expression, defined strains of Neisseria meningitidis were found to upregulate endothelial cell procoagulant activity (PCA) in a dose dependent manner. This TF response was detected with as little as 10(4) cfu/ml and reached similar levels to those seen with high concentrations of purified endotoxin (> 1 ng/ml). Treatment of N. meningitidis with either adult donor immune serum, penicillin or gentamicin failed to enhance this PCA. Limulus amoebocyte lysate assay of lipopolysaccharide in bacterial culture filtrates together with polymyxin B inhibition experiments suggest that endotoxin is largely responsible for endothelial TF induction by N. meningitidis. Incubation of endothelial cells with N. meningitidis B1940 and B1940 siaD- (an eight-fold more adherent unencapsulated isogenic strain), revealed a significantly greater TF response to B1940 siaD- (P < 0.01). In conclusion, bacterial adhesion to the vessel wall and therefore local levels of endotoxin may be important determinants of the endothelial procoagulant response to N. meningitidis and the consequent coagulopathy commonly associated with the disease.