A clinical trial was made of the efficacy of macrolide antibiotic rovamycin (spiromycin) in 30 patients (mean age 35 +/- 12 years) with moderate extrahospital pneumonia. In group I (12 patients) with affection of at least 2 lung segments rovamycin was intravenously infused for 3 days (3,000,000 IU 2 times a day), then given orally for 5 days (3,000,000 IU 2 times a day every 12 hours). 18 patients of group 2 with 1-2 affected lung segments received rovamycin per os for 5-7 days three times a day (9,000,000 IU a day). Pneumonia etiology was verified in 22 patients. Str. pneumonia, Hemophilus influenzae, Staph, aureus. Str. pyogenes were registered in 10, 3, 2, 2 cases, respectively. Five patients had associations of gram-positive and gram-negative bacteria. Hospital stay lasted 13.4 +/- 0.7 days. At the end of the second week of the treatment pneumonia resolved in 100% of patients. Rovamycin proved low toxic and well tolerated.