The effect of ganglioside GM₃ on the metabolism of phosphoinositides of human monocytoid leukemia J6-2 cells has been studied using the incorporation of[ ³²P]Pi and [ ³H]inositol into them. The results show that GM₃ inhibited the incorporation of[ ³²P] Pi and [ ³H] inositol into phosphatidylinositol (PI),stimulated the incoporation of those into phosphatidylinosito1-4,5-bisphosphate (PIP₂) and [ ³²P] Pi into phosphatidylcholine (PC), inhibited the incorporation of [ ³H] inositol into inositol phosphates (IP₃,IP₂, IP )，and of [ ³²P] Pi into phosphatidic acid (PA) in a dose-dependent manner. These results suggest that GM₃ inhibits the PI turnover of J6-2 cells.