In 22 consecutive patients treated by allogenic bone marrow transplantation, the authors report their experience in complete gastrointestinal decontamination and prophylactic systemic vancomycin. Neither septicemia from the low digestive tract nor with Gram positive is noticed. A child developed septicemia with Capnocytophaga ochracea, resistant to vancomycin. There is no infectious death in this study and no significative toxicity is reported.