Seventy-six patients with severe infection accompanying hematologic disorders including leukemia and lymphoma were treated with intravenous drip infusion of cefotetan (CTT). Of the 66 cases in whom the efficacy could be evaluated, 22 cases responded markedly and 16 cases moderately, the effective rate being 57.6%. It is impressed that more cases responded markedly to CTT than to any other antibiotics previously studied. None of the cases revealed serious side effects attributable to CTT. These results indicate that CTT is an effective and safe antibiotic for the treatment of severe infection accompanying hematologic disorders. As CTT was administered to special cases under marked decrease of neutrocyte, the importance of neutrocyte in the treatment of infection was also indicated.