The fra-2 gene is related to the proto-oncogene c-fos and encodes a member of the AP-1 transcription factor gene family. We have studied the expression of fra-2 during mouse embryonic development and compared it to the pattern of expression of other fos and jun family members. By in situ hybridization and immunohistochemical analysis we have shown fra-2 expression during late organogenesis. fra-2 transcripts are detected in several differentiating epithelia, developing cartilage and central nervous system. The pattern of fra-2 expression is distinct from that observed for other fos related genes, suggesting that fra-2 has a unique role in cellular differentiation during fetal development.