Prompt initiation of empiric antibiotic therapy is the cornerstone in the therapy of chemotherapy-induced neutropenic sepsis in cancer patients. Ceftriaxone plus gentamicin (ceftriaxone/gentamicin) is the most widely used combination of empiric antibiotics in the Department of Medical Oncology, Singapore General Hospital. However, imipenem/cilastatin has been shown to be a practical alternative. To compare the efficacy and cost effectiveness of monotherapy with our usual combination antibiotic therapy, 50 evaluable neutropenic cancer patients admitted for fever were randomised to empiric imipenem/cilastatin or ceftriaxone/gentamicin. Ceftriaxone/gentamicin was started in 24 patients. The initial clinical response rate to ceftriaxone/gentamicin was 62.5% and 84.6% to imipenem/cilastatin (P = 0.075). The average cost of antibiotics per patient started on ceftriaxone/gentamicin including cost of change of antibiotics was S$63 per day of antibiotic use and for imipenem/cilastatin it was S$252 (P < 0.02). In conclusion, although more patients receiving imipenem/cilastatin had an initial clinical response than those receiving ceftriaxone/gentamicin, this difference was not statistically significant. It would appear that imipenem/cilastatin is equivalent to ceftriaxone/gentamicin for the treatment of neutropenic sepsis. However, ceftriaxone/gentamicin was more cost effective.