Résumé : Six monoclonal antibodies(Mabs) including 4 anti-melanoma, one anti-glioma, and one anti-HLA-DR have been tested in a 125I-protein A antibody binding assay using a panel of 34 different cell lines. This panel included 19 melanomas from different clinical and geographical origins, 10 fibroblast lines out of which 9 were established from melanoma patients, 2 glial cell lines, 1 osteosarcoma, 1 teratocarcinoma, and 1 murine melanoma. The reactivity pattern of the 4 anti-melanoma Mabs showed that they were not directed against antigens strictly restricted to melanoma, but rather against antigenic structures preferentially expressed on melanoma cells. These Mabs were found to crossreact with gliomas, thus they seem to recognize neuroectoderm associated differentiation antigens. The high crossreactivity of the anti-glioma Mab for melanoma was confirmed in this study. As expected from the literature, HLA-DR antigens were found to be expressed on more than 50% of the melanoma lines tested. The cellular distribution of the antigens recognized by two anti-melanoma Mabs on melanoma cells could be visualized by an autoradiographic procedure. From the labeling pattern it was concluded that only a proportion of the cells, varying from 13 to 38%, expressed the relevant antigen.