The aim of this work is to examine if the membrane-bound Phospholipase C system is correlated with the differentiative action of Nerve Growth Factor in PC12 cells. We found that the activity of membrane-bound Phospholipase C system increased with the presence of Nerve Growth Factor at two different phases. The early phase occurs during the first minutes after the formation of Nerve Growth Factor-receptor complex and it is completed within one hour. The later phase starts two hours after Nerve Growth Factor introduction and lasts for at least a total of 48 hours. The inositol-triphosphate levels measured in intact cells by radioimmunoassay show the same pattern of activation. We think that this dual response to Nerve Growth Factor could be due to either a double separated activation of the same enzyme or the presence of two different forms of membrane-bound Phospholipase C.