In recent years, there has been a growing interest in anticancer potential of valproic acid (VPA) resulting from inhibition of histone deacetylase activity. The aim of our study was to evaluate the influence of valproic acid and cisplatin (CPT) on the growth rate of human melanoma cell lines: A375 (melanotic) and C32 (amelanotic). Both tested drugs decreased cell proliferation in a dose-dependent manner. VPA used alone significantly inhibited the growth of both cell lines at concentrations of 3 and 10 mM. Cisplatin significantly decreased cell proliferation at concentration = 0.3 microM. However, VPA enhanced the cytostatic action of CPT since simultaneous exposure of cells to 1 mM VPA and 0.1 microM CPT resulted in a significant reduction of cell growth. It can be concluded that VPA increases the sensitivity of melanoma cells to chemotherapeutic agent -- cisplatin.