Abstract Enhancing factor (EF), a growth regulatory molecule, isolated from mouse small intestines, has been well characterized in this laboratory. It increases the binding of epidermal growth factor in a unique manner via its own receptor. In the first 20 N-terminal amino acids sequenced, EF showed 50% homology to human Group II phospholipase A2 (PLA2). Here we propose that EF is yet another, unidentified isoform ofPLA2 which regulates cell proliferation via modulation of EGF binding. To our knowledge, this is the first report implicating PLA2-II-like molecules in growth regulation.