From February 1986 to July 1987, 87 patients who underwent an autologous or allogeneic bone marrow transplantation were randomized to receive ticarpen tobramycin or ticarpen moxalactam for their first febrile episode. Forty received ticarpen tobramycin and 47 ticarpen moxalactam. The two groups were similar according to age, sex, conditioning regimen, underlaying pathology and duration of granulocytopenia. We observed 58.6% of fever unknown origin and 37% of bacteremia. A similar number of clinical and bacteriological successes occurred in the two groups. Hepatic and renal toxicities were similar in the two groups. Vancomycin was widely used in these patients without particular justification. We conclude that the use of two beta lactam is a possible antibiotherapy in marrow transplantation where renal function should be preserved from additional toxicity.