The clinical efficacy and tolerability of ceftriaxone in the treatment of pneumonia and other lower respiratory tract infections were evaluated in 827 patients (515 pneumonia, 312 other lower respiratory tract infections) reported in the international literature (daily dose: 1 of 2 g.i.v. or i.m. in most patients). Therapeutic success was achieved in 738 patients (89.2%). Microbiological results were evaluated in 295 patients. Eradication of the most common respiratory pathogens was achieved in 100% of cases and of Enterobacteriaceae in 85.7%-100%. Adverse effects occurred in 4.9% of patients. A large multicenter trial was carried out in Italy using a single daily dose of 1-2 g by i.v. or i.m. Six hundred ninety-six patients were admitted to the study (370 pneumonia, and 326 other lower respiratory tract infections). Therapeutic success was achieved in 668 cases (96%). Pathogens were eradicated in 88% of cases (184 pts evaluated). Side effects were observed in 4.6% of cases.