We have investigated the relationship between in vitro cultivation of autologous melanoma metastases derived from different patients and their levels of expression of class-I and -II major histocompatibility complex (MHC) antigens and melanoma-associated antigens (MAAs). Cell cultures were established from 23 individual metastatic melanoma lesions from 10 patients and were tested early after isolation (between 3rd and 10th passages) for both constitutive expression and modulation by recombinant human leukocyte (IFN-alpha), fibroblast (IFN-beta) or immune (IFN-gamma) interferon of MHC antigens and MAA. All of the melanoma cell lines displayed altered antigen expression following IFN treatment. While in vitro cultures derived from different individuals varied in both constitutive and IFN-modified antigenic expression, cultures of autologous metastases derived from the same patient were very similar. In addition, differences in antigenic profile were apparent when early-passage in vitro cultures were compared with the same melanoma lesion, not established in culture, from which they were derived. The unique de novo and IFN-modified antigenic phenotype of cultures derived from different patients indicates that the antigenic phenotype displayed by melanoma cultures grown in vitro is genetically determined. The differences found between in vitro cultures and their corresponding in vivo lesions, as well as the antigenic heterogeneity displayed by multiple autologous melanoma lesions in vivo, suggest that the in vivo antigenic phenotype may be determined, at least in part, at an epigenetic level.