Studies in mouse, human, and chicken suggest that activation-induced deaminase (AID) is involved in three known processes leading to antibody diversification: somatic hypermutation, gene conversion, and class-switch recombination. Developing rabbit appendix provides a particularly good site for studying all three of these B cell maturation events. We report here successful cloning of rabbit AID and isolation of AID protein from rabbit appendix-cell nuclear and cytoplasmic extracts. We succeeded in identifying and locating AID protein in cells by immunohistochemical and immunofluorescent staining techniques and examined colocalization of AID and other molecules important for Ab diversification. This report extends our knowledge about AID to a mammalian species that uses gene conversion to diversify rearranged Ig genes. Although much work remains to understand fully the mechanism of action of AID and its association with other cellular components, the rabbit system now offers a particularly useful model for future studies of these dynamics.