After 3 weeks or more of treatment, 36 patients who were found to have X-ray signs of pneumonia (pulmonary infiltrative changes, fever, productive cough, weakness) were randomized into two matched groups (a study group and a control one). 77.7 and 55% of control and study group patients changed and continued antibacterial therapy. The study group patients were additionally given intravenous infusions of 400 ml of ozonized sodium chloride solution (pO3) containing 1.6 microg/ml of O3 twice weakly for 21 days. Blood ozonization considerably accelerated the resolution time of X-ray infiltrative changes so that they were undetectable in all study group patients by week 4 while they were only in 61.1% of the control groups. Blood ozonization used in combination with antibiotics permitted caused a sputum negative reaction against Chlamydia and Mycoplasma 2-3 weeks earlier. Infusions of pO3 just after the first ozonization made it possible to eliminate a clinical sign of chronic infection, such as weakness, to accelerate productive cough relief on day 10, and to reduce the number of fever patients. Ozone therapy for protracted pneumonias substantially enhances the efficiency of antibiotic treatment.