Several lectin-like activities were detected on the surface of unfixed, viable BHK cells by reaction with FITC-labelled glycosylated albumin derivatives. A prominent surface staining was obtained with the beta-lactosyl, beta-N-acetylgalactosaminyl, alpha-mannosyl and beta-N-acetylglucosaminyl derivatives. Endogenous lectin-like activities were also detected in BHK cell homogenates by haemagglutination of glutaraldehyde-fixed rabbit erythrocytes. Haemagglutinating activity was purified by chromatography of sodium deoxycholate-extracts of BHK cell microsomal fractions on Sepharose 4B and asialofetuin-Sepharose 4B. A purified agglutinin was eluted from the latter column with 0.2 M thiodigalactoside. The haemagglutination mediated by the purified factor was inhibited by thiodigalactoside, N-acetylgalactosamine, galactosyl-beta 1-4-N-acetylglucosamine and several glycoproteins. The purified agglutinin agglutinated trypsinised, fixed normal BHK cells more readily than several ricin-resistant cell lines. By contrast, a mannose-binding lectin from rabbit serum reacted equally well with normal and mutant cells. These results are in general agreement with models of cell-cell adhesion involving the interaction of surface located lectins with carbohydrate sequences of normal BHK cell surface glycoproteins.