The clinical efficacy and safety of Cefodizime (CDZM), a new cephem antibiotic, was objectively compared with that of Cefotaxime (CTX) in patients with respiratory infections under a well-controlled comparative study. Patients were administered CDZM or CTX by drip infusion b.i.d. for 14 days in principle at a daily dose of two grams. The parameters assessed were clinical efficacy, safety and clinical usefulness. The following results were obtained: 1. On the basis of committee judgement the clinical efficacy rate was 78.1% (125/160) for the CDZM group, 82.7% (124/150) for the CTX group, and no significant difference was observed between the two drug groups. On the other hand, on the basis of judgement by physicians in charge, the clinical efficacy rate was 83.1% (133/160) for the CDZM group, 83.9% (125/149) for the CTX group, and no significant difference was observed between the two groups. 2. The corresponding figures for patients with pneumonia and pulmonary suppuration were 82.4% (70/85) for the CDZM group, 79.7% (59/74) for the CTX group and no significant difference was observed according to the committee judgement. The judgement by physicians in charge also revealed 83.5% (71/85) for the CDZM group and 82.2% (60/73) for the CTX group. No significant difference was noted between the two groups. While, the committee judgement for the clinical efficacy in patients with chronic respiratory tract infections showed 73.3% (55/75) for the CDZM group, 85.5% (65/76) for the CTX group, and no significant difference was observed between the two drug groups. The corresponding figures were 82.7% (62/75) for the CDZM group, 85.5% (65/76) for the CTX group, and no significant difference was observed between the two drug groups on the judgement by physicians in charge. Furthermore, the clinical efficacy of both drugs on chronic respiratory tract infections was assessed according to "Criteria for Evaluation of Clinical Efficacy of Chemotherapeutics on Chronic Respiratory Tract Infection". It was 76.8% (53/69) for the CDZM group, 76.3% (58/76) for the CTX group, and no significant difference was observed between the two groups. 3. The bacteriological eradication rate of causative pathogens was 92.4% out of 66 patients treated with CDZM and 95.5% out of 67 patients treated with CTX in whom judgement was possible. No significant difference was observed between the two drug groups. 4. The adverse reactions occurred in 4 (2.2%) patients for the CDZM group and 8 (4.5%) patients for the CTX group respectively, with no significant inter-group difference in frequency of these reactions for all cases.(ABSTRACT TRUNCATED AT 400 WORDS)