One hundred thirty-eight patients with severe infections associated with hematopoietic disorders were treated with cefclidin (CFCL), and the efficacy and the safety of the drug were evaluated. The results obtained are summarized below. 1. Of the 126 patients in whom the efficacies were evaluable, 22 (17.5%) responded markedly well and 48 (38.1%) moderately, and the overall efficacy rate was 55.6%. 2. Efficacy rates for different infections were: 20.0% in septicemia, 61.2% in suspected septicemia, 46.7% in respiratory tract infection and 25.0% in others. 3. Significantly different efficacy ratings were observed between a group of patients with neutrophil counts of less than 100/mm3 and that with neutrophil counts of higher than 501/mm3. 4. Out of 138 patients in whom the safety was evaluable, side effects were observed in 5 patients (3.6%) and abnormal laboratory test values in 9 (6.5%). None was serious, however.