Bacterial colonization of the epithelial cells precedes infection. Mucins of the epithelial cell secretions modulate bacterial colonization. This study was designed to understand the mechanism of mucin-bacterial interactions and in particular binding between nontypeable Haemophilus influenzae and nasopharyngeal mucin(s). In an overlay assay, binding appears to be mediated by outer membrane proteins P2 and P5 of bacteria and sialic acid-containing oligosaccharides of mucin.