Type 987P-piliated Escherichia coli adhered in vitro to small intestinal villous epithelial cells and brush borders isolated from adult female rabbits, but not from infant rabbits. K99-piliated E. coli adhered to epithelial cells and brush borders from both adult and infant rabbits. 987P-negative and K99-negative E. coli as well as CFA/I-positive and CFA/I-negative E. coli failed to adhere to epithelial cells or brush borders from either adult or infant rabbits. CFA/II-positive and CFA/II-negative E. coli did not adhere to epithelial cells from infant rabbits. Pretreatment of adult rabbit brush borders with purified 987P pili inhibited adherence of piliated strain 987. Optimal adherence occurred after 15 min when brush borders and piliated strain 987 were incubated together at 25°C or 37° C in buffers at pH 7 to 8 containing 0.11 to 0.21 M total salts. A receptor-containing fraction that caused aggregation of piliated strain 987 was released into solution when brush borders were stored at 4°C. Receptor activity (aggregation) remained in solution when centrifuged at 10,000 X g for 15 min, but was sedimented at 226,000 X g for 1 h. Receptor activity was abolished by periodate oxidation and pronase digestion.