Phosphatidylinositol transfer proteins (PITPs) can bind specifically and transfer a single phosphatidylinositol (PI) molecule between phospholipid membranes in an ATP-independent manner in vitro. PITPs exist in all the eukaryotic systems from yeast to human. PITP plays an essential role in intracellular vesicle flow and inositol lipid signaling. The crystal structure of yeast PITP Sec14p reveals a large hydrophobic pocket to accommodate the acyl chains of phospholipid molecules. At the opening of the pocket, a hydrogen bond network may render Sec14p the binding specificity to PI molecules. The structure suggests that the PI-binding ability may play an important role in the in vivo function of PITPs. Copyright (C) 1999 Elsevier Science B.V.