Little is known about the physiological role and mechanism of activation of class II phosphoinositide 3-kinases (PI3Ks), although it has been shown that the PI3K-C2α isoform is activated by insulin. Using chimaeric receptor constructs which can be activated independently of endogenous receptors in transfected cells, we found that PI3K-C2α activity was stimulated to a greater extent by insulin receptors than IGF receptors in 3T3-L1 adipocytes. Activation of PI3K-C2α required an intact NPEY motif in the receptor juxtamembrane domain. We conclude that PI3K-C2α is a candidate for participation in insulin-specific intracellular signalling.