Meprins are secreted and membrane-bound metalloendopeptidases highly expressed in kidney and intestinal epithelial cells. They are oligomeric glycoproteins composed of evolutionarily related α and/or β subunits. The present work revealed that the messages for both meprin subunits were expressed in intestine and kidney in ICR and C3H/He mouse embryos (as early as day 11), indicating developmental functions for both subunits. During the first 2 weeks after birth, the mRNA levels for both subunits increased in ICR mice, but between 10 days and 3 weeks (time of weaning) the α subunit level in the intestine fell markedly. In adult ICR mice, meprin β mRNA was consistently expressed in both kidney and intestine, whereas meprin α mRNA was highly expressed in kidney but only present at low levels in intestine. In C3H/He mice, the pattern of meprin α and β subunit mRNA expression was similar to that of ICR mice, except that meprin α was barely detectable in kidney after birth. The results of postnatal studies indicate that the meprin α subunit has a role in the intestine during suckling but is not essential after weaning, and that the β homooligomer is the major meprin form after weaning in both kidney and intestine.