Exposure to alkylating agents results in the formation of a wide variety of DNA damage products. One of these, 3-methyladenine (3-mAde), is lethal if left unrepaired. The 3-methyladenine glycosylase (aMAG) gene of Arabidopsis thaliana is required for base excision repair of this lesion, and probably shares the ability of other 3-mAde glycosylases to recognize and excise a broad spectrum of damaged bases. Given the fact that DNA damage products can act as blocks to both DNA and RNA synthesis, one would expect that this protein should be expressed to some degree in all living cells. Using a DIG-labeled aMAG antisense RNA as a probe, we have investigated the developmental and tissue-specific expression of this repair gene. We found that the gene is preferentially expressed in meristematic tissue, the developing embryo and endosperm, and organ primordia. This pattern of expression is consistent with a requirement for expression in rapidly dividing tissues. However, high levels of expression were also observed in growing leaves, a tissue that is undergoing a relatively low rate of cell division. This result suggests that 3-mAde glycosylase is required not only for DNA replication, but also for cell growth.