Efficiency of ceftriaxone (Rocephin Hoffman Laroche) was assessed in 16 children aged between 3 and 14 years and in 4 adults aged between 17 and 70 years with severe infections of the urinary and respiratory tracts caused by E. coli. S. pneumoniae, P. aeruginosa, P. mirabilis or enterococci. Pyelonephritis as a sole pathology was diagnosed in 10 patients whereas in further 8 patients it complicated other diseases (nephrotic syndrome, hepatitis, cholangitis, leukemia). Pneumonia complicated nephritis leukemia or lymphoma in 8 children. Peritonitis was diagnosed in 1 adult patient. Ceftriaxone was given in a single daily dose of 50 mg/kg to all children and 2.0 g to adult patients for 7-10 days. No adverse reactions were noted. Clinical improvement was achieved in all treated patients. Cultures became negative in 17 cases after the treatment. Significant bacteremia caused by P. aeruginosa persisted in 2 patients and by E. coli in 1 patient. No toxic effects on liver, renal, pancreatic and bone marrow functioning were seen. Ceftriaxone may be safely and efficiently used for the treatment of the urinary and respiratory infections.