We analyzed the expression of 15 cancer/testis and four melanoma differentiation antigens in 21 metastatic melanoma cell lines using reverse transcriptase-polymerase chain reaction (RT-PCR) assay. On the basis of morphological characteristics, tumor cell lines were divided into three groups with high, moderate, and low grade of differentiation. Evaluation of gene expression and melanoma cell morphology has revealed a correlation between increased expression of cancer/testis genes and differentiation grade of cancer cells. The gene expression pattern for lymph node metastases and primary tumors exhibits the distribution of expression level and frequency similar to that found for established cell lines. Nevertheless, only 60% lymph node metastases or primary tumor tissue of randomly selected patients show marked expression of the most prominent cancer/testis genes, and almost 90% lesion tissue expresses at least one of 15 cancer/testis genes.