An open, randomized, multicentre study compared the efficacy and safety of 3-day azithromycin with 10-day roxithromycin for the treatment of atypical pneumonia. Azithromycin was administered 500 mg once daily to 90 and roxithromycin 150 mg bid to 60 patients. Causative pathogens were identified by serological methods. In the azithromycin treatment group, Mycoplasma pneumoniae was identified in 65, Chlamydia spp. in 9 and Coxiella burnetti in 1 patient. In the roxithromycin treatment group, M. pneumoniae was identified in 39, Chlamydia spp. in 9 and C. burnetti in 3 patients. 89 azithromycin and 53 roxithromycin patients were eligible for efficacy analysis. Clinical cure rate was 98.9% in the azithromycin and 94.3% in the roxithromycin treatment group. Adverse events were observed in 3 patients in each group. Azithromycin appears to be as effective as roxithromycin for the treatment of atypical pneumonia. The 3-day azithromycin regimen may offer an additional advantage over 10-day roxithromycin by virtue of its more convenient administration.