Macrolide and tetracycline antibiotics, which are protein synthesis inhibitors, are effective in the treatment of mycoplasma pneumonia. We evaluated the clinical efficacy and safety of roxithromycin, a new macrolide antibiotic, in the treatment of mycoplasma pneumonia. Roxithromycin was administered orally to patients who had been definitely diagnosed through Mycoplasma pneumoniae isolation or serum antibody titer as having mycoplasma pneumonia. The efficacy assessment was based on clinical signs and symptoms of infection as well as bacterial culture from clinical samples. Clinical efficacy was excellent in 6 cases, good in 6 cases and fair in 1 case, with an efficacy rate of 92.3%. The bacteriological effect was evaluated in 6 patients: the organism was eradicated in 4 cases and unchanged in 2 cases. In this study, the MIC of roxithromycin against M. pneumoniae fell in the range 0.0156-0.00625 mg/l. No adverse reaction was observed. As for abnormal laboratory findings, two cases showed elevated serum glutamic-pyruvic transaminase (S-GPT), one elevated serum glutamic-oxaloacetic transaminase and S-GPT, and one reduced neutrophil counts. From our results, we consider that roxithromycin is useful in the treatment of mycoplasma pneumonia.