A monoclonal antibody that interferes with the EDTA-resistant adhesion of Dictyostelium discoideum slug cells recognised a carbohydrate epitope on four major antigens (95, 90, 35 and 30 kDa) in slug cells. The 35 and 30 kDa antigens were specific for stalks and spores, respectively. The 30 kDa antigen was identified as the cell surface glycoprotein, PsA. Cyclic AMP, acting via cell surface receptors, induced only the 90 kDa slug cell antigen. Slug cell adhesion proteins may be involved in cell-sorting and the glycosylation of the 95 and 90 kDa antigens appeared to be abnormal in a mutant defective in cell-sorting. Previously, a 150 kDa glycoprotein has been strongly implicated in slug cell adhesion and the present work suggests that additional glycoprotein(s) are involved.