FIPI is a potent and selective phospholipase D inhibitor. FIPI attenuate mercury-induced lipid signaling leading to protection against cytotoxicity in aortic endothelial cells. FIPI rapidly blocks in vivo PA production with subnanomolar potency. We were surprised to find that several biological processes blocked by 1-butanol are not affected by FIPI, suggesting the need for re-evaluation of proposed FIPI does inhibit PLD regulation of F-actin cytoskeleton reorganization, cell spreading, and chemotaxis, indicating potential utility for it as a therapeutic for autoimmunity and cancer metastasis.