Phosphoinositide 3-kinases (PI 3-kinases) have critical roles in diverse cellular signaling processes and in protein trafficking, In contrast to the class I PI 3-kinases alpha, beta, and delta which bind via src homology 2 (SH2) domains of adaptor proteins to tyrosine kinase receptors, the mechanism of recruitment of the PI 3-kinase gamma to membranes is unknown. We report in vitro experiments using immobilized proteins and small unilamellar vesicles which suggest an involvement of anionic phospholipids in membrane association of PI 3-kinase gamma, Furthermore we provide evidence that the enzyme displays beside the catalytic center a phospholipid binding domain which is essential for enzyme activity.