Mouse monoclonal antibody AbR.sub.24 (Dippold et al., Proc. Natl. Acad. Sci. 77:6114-6118, 1980) has a high degree of specificity for human melanoma cells when tested on viable cultured cells using the PA-MHA serological assay. The antigen detected by this antibody has been isolated from melanoma cells and shown to be G.sub.D3 ganglioside by compositional and partial structural analysis and by comparison with authentic G.sub.D3 by thin layer chromatography (TLC). AbR.sub.24 reacts with authentic G.sub.D3, but not with any other ganglioside tested. Using TLC and reactivity with AbR.sub.24, a wide range of cells and tissues was examined for the presence of G.sub.D3. A new serological assay, termed glycolipid-mediated immune adherence (GMIA), was devised for assaying the reactivity of AbR.sub.24 with gangliosides. Melanomas (cultured cells or tumor tissue) were shown to have T.sub.D3 and G.sub.M3 as major gangliosides. Other cells and tissues examined also contained G.sub.D3, but usually only in low amounts. Melanomas (and MOLT-4, a T-cell line) were characterized by a simplified ganglioside profile with G.sub.D3 and G.sub.M3 as major components. The apparent discrepancy between the ubiquitous presence of G.sub.D3 and the serological specificity of AbR.sub.24 for melanoma cells can be explained in terms of localization and concentration of G.sub.D3 in different cells.