Mycoplasma pneumoniae and M. gallisepticum possess binding sites of protein nature which mediate attachment to neuraminidase-sensitive regions on both respiratory epithelium and red blood cells. The binding sites of these organisms are similar though not identical. Several approaches were applied for the isolation of the binding sites. Of these, the use of affinity chromatography yield the least complex protein fraction. We have recently been using sialoglycopeptides as the ligands in affinity chromatography. The availability of monoclonal antibodies which inhibit the attachment of M. pneumoniae to host cells should provide a very specific tool for the isolation of the attachment moiety. It should be mentioned that not all mycoplasmas adhere to host cells via sialic acid specific receptors, and other approaches should be developed to study these mycoplasmas' attachment moieties.