Experimental data are provided which demonstrate the inhibitory effects of penta-acetyl geniposide, (Ac)5-GP, on the growth and development of C-6 glioma cells inoculated into rats. In the pretreatment experiments, (Ac)5-GP prolonged the latency period of T50 (time for 50% tumour incidence). At week 7, the growth inhibition was 41% with 5 mg/kg and 75% with 10 mg/kg of (Ac)5-GP. In the post-treatment experiments, growth inhibition was less. No significant hepatotoxic effects were observed in the treated group, indicated by the constant levels of serum enzymes (e.g. asparate aminotransferase). We suggest that (Ac)5-GP is a potent chemopreventive agent on glioma cells.