Macrophages are cleared from the inflamed peritoneal cavity by active emigration through the mesothelial lining to the draining lymph nodes and this represents a key aspect of the resolution of the inflammatory response. We have previously shown in murine models that the clearance of inflammatory macrophages from resolving acute peritonitis is rapid (half-life 14 days). The mechanisms which control the differences in these rates of clearance are unknown but we hypothesized that macrophage adhesion interactions may regulate inflammatory cell clearance. To determine if macrophage adhesion altered during the course of peritonitis we examined the ability of macrophages lavaged at different times over the course of acute peritonitis to adhere to mesothelial cells in vitro. In our murine model of acute peritonitis — i.p. 4% Brewers thioglycollate (TG), macrophage numbers were shown to peak within the peritoneum at day 5 after challenge and decline to control levels by day 10 through to day 14. Inflammatory cells (>92% macrophages) were collected at 5–14 days after challenge, fluorescently labelled with the cell tracking dye CMFDA, and added in equal numbers (1×105 cells well−1) to confluent monolayers of mesothelial cells (transformed mesothelial cell line — Met5A) in 96 well culture plates. After 45 min adhesion, non-adherent cells were washed off and the number of adhered cells determined using a fluorescent plate reader. With adhesion of non-inflamed resident macrophages taken as control, the macrophage population lavaged 5 days after TG challenge exhibited a 31 (3.4)% (mean (SD)) [E4]greater[/E4] adhesion to the mesothelial layer than controls, this had decreased to 26 (5.2)% [E4]less[/E4] than controls by day 14 (P