Cefaclor was used to treat 13 children with acute otitis media caused by ampicillin-resistant strains of Hemophilus influenzae. The children were re-examined on days 4, 10, and 28. Pharmacologic compliance was assessed by means of a bioinhibition assay on a urine specimen obtained on days 4, 7, and 10. Nine of the 13 children had evidence by tympanogram of residual otitis media with effusion (secretory otitis media). Of these, three were noted to have a bulging, yellow or grey eardrum, which suggested an ongoing acute process. A second middle ear culture was obtained from two of the 3 children, but no pathogens were recovered. Two others had recurrence of otitis shortly after cessation of therapy. Cefaclor is an acceptable antibiotic for the treatment of ampicillin-resistant acute otitis media; but, after cefaclor therapy, some children continued to have a bulging eardrum and sterile pus in the middle ear or had recurrences of otitis soon after cessation of therapy.