• A randomized clinical trial compared cefaclor and amoxicillin for the treatment of acute otitis media (AOM). Twenty-four (77%) of the 31 examinable patients treated with cefaclor and 25 (83%) of the 30 examinable patients treated with amoxicillin had resolution of signs and symptoms after completing a ten- to 14-day course of the antibiotic. Patients who had bilateral AOM, serous or mucold middle ear effusion, Hemophilus influenzae cultured from effusion, or more than five previous otitis media episodes, or who were 3 years of age or younger were more likely to fail treatment. Hemophilus influenzae isolated from effusion were significantly less susceptible to cefaclor than amoxicillin, but none of the 12 treatment failures were caused by antibiotic-resistant infections. Eight (36%) of the 22 patients who recovered after treatment and were reexamined one to three weeks later experienced recurrent AOM. Ear-specific, as well as patient-specific, analyses showed no significant differences between cefaclor and amoxicillin.