Imipenem/cilastatin sodium (IPM/CS), which has a broad spectrum of activity against both Gram-positive and -negative bacteria including methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa, was used as the second choice for severe infections associated with hematological disorders. Sixty-five patients were treated with IPM/CS. Among them, 53 patients were evaluable for the clinical efficacy. Twelve patients were not evaluable due to the following reasons: 5 patients were treated with combinations of other regimens such as cefzonam, cefmenoxime, ciprofloxacin or gamma-globulin, 5 were patients to whom IPM/CS was administered as the first choice, and the remaining 2 patients were thought to be suffering not from febrile infections but from febrile tumor. Excellent responses were observed in 10 (18.9%) patients and good responses in 23 (43.4%) patients, with an overall rate of efficacy of 62.3%. The efficacy in septic patients was 75% (3/4), and that in patients whose peripheral granulocytes were continuously below 100/microliter was also 75% (6/8). Two patients who suffered from tumor fever and 5 patients who had received no chemotherapy before IPM/CS administration were included in the final evaluation of side effects. Side effects were observed in 16 patients (16/60, 26.7%). In a 61 years, female patient, a skin eruption was found 4 days after IPM/CS therapy was started. In 15 patients, mild gastrointestinal symptoms such as nausea and vomiting were identified within a few days after IPM/CS treatment was started. Abnormal laboratory data such as eosinophilia, liver dysfunction or renal dysfunction were also identified in 4 patients (4/60, 6.7%). Degrees of these abnormalities were very slight, however, and the continuation of treatment was not disturbed. These results indicated that IPM/CS was an effective second line regimen of chemotherapy for the treatment of severe infections in patients with hematological disorders.