During early development in mouse and Xenopus, translational activation of stored maternal mRNAs by cytoplasmic polyadenylation requires both the nuclear polyadenylation signal AAUAAA and U-rich cis-acting adenylation control elements (ACEs), also termed cytoplasmic polyadenylation elements, located in the 3' UTR. Using an ACE-based PCR strategy (Sallés et al., 1992) we have isolated two novel cDNAs from mouse oocytes: OM2a and OM2b (for Oocyte Maturation). Each message contains an ACE consensus sequence upstream of AAUAAA, is specifically transcribed in the growing oocyte, and is cytoplasmically polyadenylated upon oocyte maturation. Comparison of the mouse and rat homologs reveals considerable nucleotide sequence homology and conservation of overall gene organization. However, the predicted open reading frames are far less conserved, suggesting that these genes may not be functioning as proteins. The tissue specificity and tight temporal regulation of the RNAs suggest a role for these genes during early development.