Escherichia coli RDEC-1 (serotype O15:H-) is a rabbit enteropathogen in whichin vivoenteroadherence is both site specific and age related. To determine whether these differences could be related to mucins, we evaluated inhibition of binding of AF/R1 piliated RDEC-1 by mucins isolated from various segments of intestine of rabbits at different ages. Mucin was purified from intestinal crude mucus by cesium chloride serial ultracentrifugation. RDEC-1 was grown to promote the expression of hydrophobic mannose-resistant AF/R1 pili. Quantitation ofin vitrobacterial binding was determined using a crystal violet colorimetric assay. In postweanling rabbits, inhibition of RDEC-1 binding by purified mucin derived from ileal segments (45.1 ± 2.6%, mean ± SEM) and proximal colonic segments (46.0 ± 5.5%) was less than purified mucins derived from jejunal segments (70.0 ± 2.0%) and distal colonic segments (71.0 ± 3.7%,p< 0.05) of the intestinal tract. In all age groups, mucins derived from jejunal segments inhibited RDEC-1 binding to a greater level than mucins derived from ileal segments. In addition, inhibition of binding by mucin derived from proximal small intestine of postweanling rabbits (70.0 ± 2.0%) was greater than that of weanling rabbits (55.2 ± 3.5%,p< 0.05) with suckling rabbit inhibition (62.1 ± 3.5%) between these two levels. We conclude that mucin inhibition of RDEC-1 adhesion is both age and region related and therefore may contribute to both age-related and site localization of bacterial infections of the intestinal tract.