Using developing rat cerebellum, we examined the correlation between the turnover of phosphoinositide (PI) and c-myc expression. The 32P incorporation into polyphosphoinositides changed remarkably with advancing age. It reached a maximum value on PND 7, and then decreased gradually until PND 14. Immunostaining by anti-PIP2 antibody changed in parallel. The expression of c-myc mRNA was also changed developmentally, showing a peak on PND 7; whereas c-MYC protein expression showed a peak on PND 10. Together, these results suggest that c-myc expression is regulated by PI turnover during the early developing stage of rat cerebellum.