The fraction of proteins capable of binding to photoreceptor membranes in a Ca2+-dependent manner was isolated from bovine rod outer segments. One of these proteins with apparent molecular mass of 32 kD (p32) was purified to homogeneity and identified as annexin IV (endonexin) by MALDI-TOF mass-spectrometry. In immunoblot, annexin IV purified from bovine rod outer segments cross-reacted with antibodies against annexin IV from bovine liver. This is the first detection of annexin IV in vertebrate retina.