The gangliosides in human diploid fibroblasts--TIG-1, TIG-7, and IMR-90--were analysed at different cell densities at early and late passages to clarify the relationship between age and cell density dependent changes of the gangliosides. In early passages, the ganglioside concentrations increased with increase in cell density. At late passages, however, the concentrations were lower than those at the early passages either in the growing or confluent phase, and slightly increased with increase in cell density. The pattern of ganglioside compositions were apparently different between early and late passage cells either in growing or confluent state. In the early passages, GM3 and GD3 were major constituents, and GM2, GD1a, or the other more complex gangliosides were detected as minor components. With increase in cell density, the content of GM3 decreased, whereas GD3 and the others increased. At the late passages, however, GM3 was the major component, and GD3, GM2, or GD1a were minor, but the others were hardly detectable. The ganglioside pattern did not change with increase in cell density. Thus, the age-dependent changes of gangliosides could be distinguished from the cell density dependent alterations.