The safety and efficacy of a new oral suspension formulation of clarithromycin were evaluated in this multicenter, Phase III, single blind, comparative trial in 379 children ages 6 months to 12 years with signs or symptoms of acute otitis media. Children were randomized to receive a 10-day course of clarithromycin oral suspension (7.5 mg/kg; maximum, 500 mg) or cefaclor oral suspension (20 mg/kg; maximum, 500 mg) twice daily. Specific clinical response criteria were developed based on pretreatment signs and symptoms and results of tympanometry. Of the 379 enrolled patients 281 (74%) were evaluable (clarithromycin, 150; cefaclor, 131). There were no demographic differences between the two groups. Fifty percent of the patients had 2 to 4 episodes of otitis media (including the current episode) in the past 12 months; 63% of the patients had an infection of moderate severity. Clarithromycin and cefaclor suspensions were similarly effective for the treatment of acute otitis media. Clinical success (cure, cure with effusion or improvement) was achieved in 86% of clarithromycin-treated patients and 90% of cefaclor-treated patients. The majority of bacterial isolates for which susceptibility results were available were fully or moderately susceptible to the study drugs (96% clarithromycin, 92% cefaclor). Both drugs were welltolerated; adverse events considered probably study drug-related were reported by 30 (15%) of clarithromycin recipients and 31 (17%) of cefaclor recipients. There were no significant differences between the groups in the numbers of patients reporting events that were thought to be related to study medication. A 10-day regimen of clarithromycin suspension (7.5 mg/kg twice daily) appears to be as safe and effective as a 10-day regimen of cefaclor suspension (20 mg/kg twice daily) for the treatment of acute otitis media in children.