One hundred thirty-eight patients with severe infections accompanying hematological diseases were treated with cefodizime (CDZM). CDZM was administered by intravenous injection at daily doses ranging from 2 g to 8 g for about 3 to 18 days. Clinical efficacies of CDZM were excellent in 30 cases, good in 37 cases, fair in 1 case and poor in 53 cases. The efficacy rate was 55.4%. The efficacy rate was 56.4% in patients from whom causative organisms were not identified. The efficacy rate against Gram-negative bacteria (66.7%) was higher than that against Gram-positive bacteria (28.6%). No significant differences in the efficacy rates were found among groups of patients with different initial neutrophil counts (less than 100, 100-499, and over 500/microliters). Skin eruption caused by CDZM was observed in 2 patients (1.5%). Hepatic disorders, renal dysfunction and urinary test abnormality (protein and urobilinogen) were observed in 7 (5.0%), 1 (0.7%) and 1 (0.7%), respectively. Therefore, CDZM was considered to be a clinically useful antibiotic for severe infections complicated with hematological diseases.