The efficacy of a combination of cefaclor and fosfomycin otic solution was investigated in 81 children with acute otitis media, who needed myringotomy for severe erythema and swelling of the tympanic membrane. The patients were followed up for one year to investigate correlations between test findings of early treatment and both clinical course and prognosis. These drugs were used for 10 days, and the effects of combined use were evaluated from findings in the tympanic membrane after the 10-day period. Three stages were assessed; cured, recovered and unchanged. In cured and recovered cases, the administration was evaluated to be effective. Within 2 weeks after the start of treatment, views of the ears, nose and epipharynx were roentgenographically examined for shadows of mastoid pneumatization and the paranasal sinuses, and the presence or absence of adenoid vegetation. After the antibiotic administration, the patients were instructed to visit us at least once every 3 months to rule out recurrence of acute otitis media and otitis media with effusion (possibly occurring one year after treatment). The following results were obtained. 1. The two drug combination was effective in 99% of patients, produced no side effects, and was deemed extremely useful. 2. The course of acute otitis media tended to be significantly prolonged in patients with mastoid pneumatization and paranasal sinus shadows as revealed by roentgenography.(ABSTRACT TRUNCATED AT 250 WORDS)