We have examined the patterns of expression of members of the fos and jun families of transcription factors during murine postnatal intestinal development. Northern analysis showed increases in fos B, c-fos, and jun B mRNA levels in both proximal jejunum and colon. These increases coincide with weaning, a period of major changes in intestinal cell proliferation and migration. Administration of dexamethasone to suckling mice resulted in transient induction of c-fos mRNA levels in all gut segments. Thus, modifications in expression of certain members of the fos and jun families in vivo correlate with major maturational changes during murine intestinal development and support a role for these transcription factors in the regulation of intestinal functions.