PC12 cells grow in serum-free medium (SFM) if high doses of insulin (5-50 μg/ml), or combined insulin (5 μg/ml) and insulin-like growth factor-I (3 ng/ml) are added daily. Ganglioside GMl counteracts these effects in a dose-responsive fashion between 10 nM and 50 μM. This provides a serum-free system to study the interactive effects of gangliosides on growth and neuritogenesis in PC12 cells.