Polarized intestinal epithelial cells are characterized by the presence of a brush border at their apical surface. The brush border cytoskeleton is assembled during cell differentiation and is composed of parallel actin bundles, held together by specific actin-binding proteins. Using specific cDNA probes we have studied the expression of the mRNAs encoding ezrin and moesin, two members of a class of proteins that connect the microvillar cytoskeleton to the plasma membrane, during the process of enterocyte maturation that occurs both in the embryonic and in the adult small intestine, along the crypt-villus axis. The steady state levels of ezrin mRNA were found to increase in the fetal gut epithelium between day 15 and day 20 of gestation and during the first week after birth, in parallel with the morphogenetic process that leads to cell polarization and brush border assembly. On the contrary, moesin mRNA is expressed at very low levels in the mature small intestine, with a sudden drop in transcription occurring at birth. In the continuously renewing epithelium of adult animals, ezrin mRNA levels are higher in the differentiated villus cells of the distal portions of the gastrointestinal tract and very low in undifferentiated crypt cells. These data demonstrate that the expression of the ezrin gene is regulated at the level of mRNA abundance during development and differentiation of the intestinal epithelium.