Chronic inflammatory conditions such as colitis are associated with an increased risk of developing adenocarcinoma (Rutter et al. 2004). Current evidence suggests that colitis occurs due to an aberrant immune response to enteric flora (Mahida & Rolfe, 2004). Bacterial toxins such as endotoxin have potent proinflammatory effects through activation of toll-like receptor 4 (TLR4) (Beutler, 2004). In this study we examined the role of TLR4 signalling in a model of colitis-associated adenocarcinoma; the interleukin-10-deficient (IL-10^-/-) mouse. Wild type (WT), IL-10^-/- or IL-10^-/-/TLR4^-/- mice were studied at 3 months for signs of colitis. Inflammation was assessed using macroscopic and histological scoring systems. Neoplastic changes were assessed using macroscopic mucosal polyp score and histological identification (epithelial hyperplasia, aberrant crypt foci, abnormal crypt formation, submucosal invasion of crypts, neoplastic nuclei). Chemokines were measured by Rnase protected assay (RPA). Leukocyte kinetics were measured in colonic mucosal venules of anaesthetized mice (intravenous ketamine 200 mg/kg and xylazine 10 mg/kg) using intravital microscopy. IL-10^-/- mice had significantly increased macroscopic (3.9+0.3) and microscopic scores (5.5+0.4) over WT mice (0.6+0.03 and 0.8+0.2, respectively). In IL-10^-/-/TLR4^-/- mice a small but significant increase in macroscopic (4.8+0.4) and histological (6.6+0.3) scores was observed over IL-10^-/- mice. No significant difference in granulocyte infiltration (myeloperoxidase assay) was observed between the mutant mice. Interestingly, mucosal hyperplasia in the form of polyps was significantly increased the double mutant mice (p<0.05) and histological examination noted increased neoplasia scores (4.8+0.5 vs 3.3+0.5 respectively). These neoplastic histological changes were associated with an increased incidence of adenocarcinoma (submucosal invasion of neoplastic crypts) in the absence of TLR4 (10/19 vs 1/8 IL-10^-/- mice). Concomitantly, IL-10^-/-/TLR4^-/- mice had significantly lower chemokine levels (e.g. RANTES, MIP-1α,β, MCP-1, Tac-3 and IP10, p<0.05) than IL-10^-/- mice. In vivo leukocyte kinetics showed enhanced rolling flux (p<0.05) and no difference in adherent leukocytes in the absence of TLR4. The absence of TLR4 promotes colitis-associated adenocarcinoma in IL-10^-/- mice. Our data suggest that TLR4-dependent chemokine synthesis plays a part in modulating colitis-associated neoplasia development perhaps through altered leukocyte recruitment.