Serum protein S100 and melanoma-inhibitory protein (MIA) have been described as useful tumor markers for malignant melanoma. In this study, these two serum proteins were compared in 48 patients with melanoma at different stages of disease. Serum concentrations of S100 and MIA were measured by immunoradiometric and enzyme-linked immunosorbent assays, respectively. We found that the cut-off values were 17.4 ng/ml for MIA and 0.09 microg/l for S100. Five patients had stage I-II, 22 had stage III, and 21 had stage IV disease. Serum levels of two markers were elevated with metastatic disease (p < 0.05). Sensitivities of the MIA were found higher compared with S100 in patients with extensive (M1c) metastatic disease and with chemotherapy nonresponders (p > 0.05). We showed a trend for worsened outcome in patients with elevated MIA level in univariate analysis. MIA was found to be more sensitive and is a potential prognostic marker for patients with metastatic malignant melanoma in comparison with S100.