Cefuroxime axetil, a new beta-lactamase-stable cephalosporin, was compared with cefaclor for the treatment of acute bacterial maxillary sinusitis in 106 adult patients. Direct sinus aspirations for quantitative bacterial culture were done for all patients before treatment; aspiration was repeated for most patients after treatment. Pretreatment sinus aspirates were positive for 63 of 134 sampled sinuses. Of specimens yielding at least 10(4) CFU/mL, Haemophilus influenzae (38%) and Streptococcus pneumoniae (37%) were the most common pathogens. Ten (42%) of 24 strains of H influenzae, 2 (40%) of 5 Haemophilus parainfluenzae, and all 3 isolates (60%) of Branhamella catarrhalis produced beta-lactamase. Cefuroxime axetil, 250 mg twice a day, was compared with cefaclor, 500 mg three times a day. Among culture-positive sinuses, bacteriologic cure was achieved in 36 (95%) of 38 sinuses and 15 (71%) of 21 sinuses treated with cefuroxime axetil and cefaclor, respectively. The overall frequencies of adverse events were similar between drugs, although cefuroxime axetil was associated with more frequent diarrhea. Cefuroxime axetil was an effective therapy for the treatment of acute bacterial maxillary sinusitis in adults.