The structural analysis of neutral glycolipids and gangliosides of the SV40-transformed Balb/c3T3 cells (SV3T3 cells) and concanavalin A-selected SV3T3 revertant cells, compared with untransformed Balb/c3T3 cells, has shown: a content of neutral glycolipids in revertant cells near to that found in the untransformed parental cells, a similar decrease of the higher gangliosides in transformed and revertant cells and a content of ganglioside GM3 in revertant cells much higher than that found in SV3T3 and untransformed Balb/c3T3 cells. The possible role of ganglioside GM3 in growth control is discussed.