Forty-three patients with severe infections which were complicating hematological disorders were treated with panipenem/betamipron, and the efficacy and the safety of the drug were evaluated. The results obtained are summarized below. 1. Out of 40 patients in whom efficacies are evaluable, the clinical responses were excellent in 17 patients, good in 4, fair in 7 and poor in 12, and the total clinical efficacy rate was 52.5%. 2. The efficacy rate in 7 patients who had failed to respond to prior treatment with other antibiotics was 57.1%. Thus, no significant difference was observed in efficacy rates between the patients who had failed to respond to prior treatment with other antibiotics and the patients who received no preceding antibiotics therapy. 3. Out of the 43 patients in whom the safety was evaluable, no side effects nor abnormal laboratory findings were found.