Cytostatic and cytotoxic effects of recombinant tumor necrosis factor-alpha on sensitive human melanoma cells in vitro may result in selection of cells with enhanced markers of malignancy. Monolayer cultures of the human melanoma cell lines StML-12, StML-11, StML-14 (third, respectively, twenty-fifth subculture), and SKMel-28 derived from specimens representing different stages of tumor progression were treated with 10-10,000 U/ml rTNF-alpha applied for 72 h. The effects of rTNF-alpha on cell proliferation, DNA synthesis, cell viability, cloning efficiency, cell division, cell morphology, and the immunophenotype were studied in triplicate experiments. The cell line StML-14(3) revealed a significantly dose-dependent reduction of growth due to both cytostatic and cytotoxic activities of rTNF-alpha as well as a decrease of CE. Increased numbers of cells in prophase were observed 24 h after addition of r-TNF-alpha. In addition, dislocation of chromosomes in the metaphase, formation of micronuclei, and dose-dependent increases of cells exhibiting micronuclei and the DNA amount per cell were detected at the end of treatment. On the other hand, only a slight sensitivity to the anti-proliferative effect of rTNF-alpha was observed with StML-14(25) and SKMel-28, whereas StML-12 and StML-11 were significantly resistant. The last four cell lines were serially subcultivated and presented common phenotypic patterns with more malignant characteristics than the cell line StML-14(3) before treatment. Overall, rTNF-alpha enhanced the malignant immunophenotype of the cell lines tested. It increased the expression of the "late" melanoma progression markers A.10.33 and A.1.43, and Ki67, and it decreased the expression of the "early" progression marker K.1.2. The expression of HLA-I, HLA-DR, and ICAM-1 was also enhanced after rTNF-alpha treatment, whereas in contrast to other cytokines, rTNF-alpha did not induce the de novo expression of HLA-DR in HLA-DR-negative melanoma cell lines. These findings indicate that rTNF-alpha induces cytostasis and decreases cell viability of certain rTNF-alpha-sensitive melanoma cells. These effects may result in selection of rTNF-alpha-non-sensitive human melanoma cell populations with higher proliferation rates and a more aggressive immunophenotype in vitro. 