Attachment of Streptococcus pneumoniae and Haemophilus influenzae to epithelial cells on the posterior wall of the nasopharynx (NPH) was determined in 10 healthy children, culture-positive for either of these microorganisms. By using immunofluorescence technique and specific fluorescein-labelled antisera against these microorganisms, it was shown that in only 2 of the children studied were these pathogens firmly attached to the non-ciliated cells of the NPH. Attachment of S. pneumoniae and H. influenzae to the epithelial cells close to the nasopharyngeal opening of the Eustachian tube is of the utmost importance for the development of invasive disease, especially acute otitis media. Attachment of these pathogens to the epithelial cells covering the adenoid tissue may naturally be of significance for the induction of specific antibody production against these microorganisms.