Immunohistological methods were used to examine the relation between the metastatic potential of melanoma and expression of the neuroglandular antigen (CD63) and other members of this family of molecules, CD53, CD37, CD9 and the target of an anti-proliferative antibody (TAPA-1), as well as MHC-class-I and -II antigens. The criteria used to establish metastatic potential were their relation to thickness of the primary melanoma, and differences in expression between vertical and radial growth phases of primary melanoma and between primary and metastatic melanoma. Studies on basal-cell carcinoma (BCC) and squamous-cell carcinoma (SCC) were also included as controls for malignant skin cancers with low metastatic potential. Expression of CD9 and MHC-class-1 antigen was found to be inversely related to thickness of the primary tumor, and CD9 was expressed predominantly on primary rather than on metastatic tumors. CD9 expression correlated with MHC-class-1 expression on melanoma, and both were expressed on BCCs and SCCs having low metastatic potential, but not on compound nevi. CD63 and TAPA-1 were expressed on nevi but not on SCC and BCC. Leu 13 is a molecule associated with TAPA-1 in lymphomas, and was found to be expressed in sections from 5 out of 34 primary and 5 out of 21 metastatic melanoma. CD53 and CD37 were not detected on melanoma. Our results indicate that several members of the neuroglandular antigen are expressed in melanoma and that low expression of CD9 on primary melanomas might have prognostic significance with respect to the potential for metastasis.