Glycosphingolipids are plasma membrane macromolecules involved in diversified recognition functions on the cell surface resulting in modulation of cell adhesion and differentiation. As the in vitro cellular system of the neoplastic cell line SGS/4A and syngeneic normal fibroblasts (FG) represents a useful tool for studies on molecular mechanisms regulating cell adhesion, neoplastic transformation and cellular ageing, we studied the changes of glycosphingolipid and of the enzymes involved in their metabolism in both cultured cells at different subculture stages. The FG subculture progression induces a drastic decrease of total glycosphingolipid content with consistent alterations in the molecular composition. In particular, a significant decrease of GM3, a slight increase of GD1a, the disappearance of ‘b’-series gangliosides and the drastic reduction of triosylceramides were observed. On the contrary, the increasing number of SGS/4A subcultures, characterized by a specific and different glycosphingolipid composition as compared with FG cells, does not cause modifications. Although glycosyltransferase activity levels quite well parallel the glycosphingolipid patterns and can account for the noted variations, the mRNA expression analysis of two glycosyltransferases suggests that the in vitro cell ageing of normal rat fibroblasts causes drastic changes in the glycosphingolipid profile through the regulation, at either the transcriptional or post-translational level, of some biosynthetic enzymes.