Abstract In this paper, we characterize the binding of N-acetyl-β-D-glucosaminidase to membranes of rat liver during development. Cation-independent phosphomannosyl receptors were shown to be involved in the recognition of the enzyme at the following ages: 18 days of fetal life, 10-, 30- and 90-day-old rats. We remark here two important differences in the binding of the fetal enzyme when compared with that in 90-day-old rats; (a) in addition to an optimal binding at pH 7.0, the fetal enzyme showed another peak of binding at acidic pH (5.0), and (b) the binding of the fetal enzyme was also inhibited by galactose-6-phosphate. This inhibition was higher than that of mannose-6-phosphate at the acidic pH. We concluded that the lysosomal enzymes and their receptors undergo important changes around birth.