A multi-institutional study was conducted between September 1990 and April 1992 to evaluate the efficacy and toxicity of imipenem/cilastatin sodium (IPM/CS) in severe infections in cases of granulocytopenia in children with hematological diseases and cancers. A total of 60 episodes of infection were treated with the drug, and an overall efficacy rate of 80% (48/60) was obtained. The efficacy rate in patients who were positive for Endospecy test was 90.0%. A group of patients who had previously received other antibiotics showed an efficacy rate of 79.2%, while the patients who had not received previous antibiotic treatment showed an efficacy rate of 80.6%. The difference between the 2 groups was statistically insignificant, however. Granulocyte counts appeared to have influence on the efficacy of the drug, but the influence was not strong. Three patients had nausea, vomiting and/or diarrhea, and 2 other patients showed abnormal liver function test parameters though they recovered soon after the cessation of the drug treatment. From these results, we have concluded that IPM/CS is an effective antibiotic for treatment of severe infections with hematological diseases and cancers in children.