The luminal plasmalemma of regenerating mesothelial cells was examined by transmission electron microscopy and the concentration of microvilli at various stages of healing was quantified. Charged tracer and lectin binding techniques were also employed to investigate electrostatic and chemical changes in mesothelial glycocalyx. In uninjured mesothelium and a t all stages of healing, the concentration of microvilli at the cellular periphery was greater than over the main cell mass (Pc0.05). Furthermore, there was an increase in the concentration of microvilli in all regions by day 4, which reached a maximum at day 6, then a t days 10-15 returned to values closer to uninjured mesothelium (PCO.01). These changes were associated with an alteration in surface charge. In all lesions, the surface charge on microvillar membranes was greater than for flat membranes, but the difference was only significant a t days 4, 6, and 15 (P<O.OOl). The changes in surface charge may reflect a differential expression of mucopolysaccharides on the surface membrane. In addition, concanavalin A bound avidly to mesothelial surface membranes, suggesting the presence of a-methyl-D-mannoside residues. These findings suggest an association between microvillar formation and surface charge, the former protecting the healing mesothelium by enhancing entrapment of serosal fluid and its contents.