A prospective, open, noncomparative study was conducted to assess the efficacy and safety of azithromycin given once daily for 3 or 5 days to eradicate Bordetella pertussis from the upper respiratory tract of infants and young children. Seventeen children received azithromycin in a dose of 10 mg/kg on day 1 followed by 5 mg/kg once daily for four consecutive days, and 20 were given 10 mg/kg once daily for 3 days. Seven days after the initiation of therapy, 33 of 35 (94.3%) patients had negative cultures for Bordetella pertussis. On day 14, cultures from all 34 evaluable patients were negative. These findings suggest that a controlled, comparative study of erythromycin versus short-term administration of azithromycin is justified.