FAIM1 (or Fas Apoptotic Inhibitory Molecule 1) is a recently discovered negative regulator of apoptosis. FAIM1 has no significant regions of homology to other gene products that modulate Fas killing. It plays a role as an inducible effector molecule that mediates Fas resistance produced by surface Ig engagement in B cells. Overexpression of FAIM1 diminishes sensitivity to Fas mediated apoptosis of B and non B cell lines. FAIM1 is highly evolutionarily conserved and is widely expressed in murine tissues, suggesting that FAIM1 plays an important role in cellular physiology.