The ganglioside composition of human malignant melanoma was studied with the use of 80 melanoma specimens, including 52 surgical specimens and 28 cultured cell lines. A ganglioside fraction was isolated and purified from each of these tissues, and the amount of each component ganglioside was assessed by thin-layer chromatography (TLC) and a TLC scanner. Five gangliosides (GM3, GD3, GM2, GD2, and alkali-labile ganglioside) were most commonly expressed by these melanomas. However, the total ganglioside amount (ranging from 33 to 302 micrograms/g wet wt of tissue) as well as the distribution of each ganglioside were widely heterogeneous in both biopsied and cultured melanomas. When the ganglioside expressions of cultured and biopsied melanomas were compared, GM2 and GD2 were minor components of biopsied melanomas but often became major components of cultured melanoma cells. Conversely, alkali-labile ganglioside was expressed more strongly on biopsied melanomas. This heterogeneity suggests that it will be necessary to analyze the ganglioside composition of biopsied melanomas before using monoclonal antibodies to melanoma-associated gangliosides for melanoma diagnosis or therapy.