Fourty-one patients with haematological malignancies or severe aplastic anaemia underwent allogeneic or syngeneic bone marrow transplantation and received one of two forms of infection prophylaxis while granulocytopenic: total decontamination in strict reverse isolation (ITD, 26 patients) or selective decontamination of the digestive tract with barrier nursing (SD, 15 patients). The patients were evaluated for infection acquisition, fever days, days on systemic antibiotics and granulocyte transfusions from 48 hours after the beginning of the decontamination procedure until 1,000 granulocytes/microliter have been reached. Ten of 26 patients of the ITD group remained free of febrile episodes and infections, whereas all patients of the SD group acquired infections (p less than 0.001). During granulocytopenia patients of the ITD group had fewer fever days, were less frequently on systemic antibiotics and received fewer granulocyte transfusions as compared with the SD group. Both methods were obviously very effective in preventing gram-negative infections, infections caused by Staphylococcus aureus and infections due to yeasts or fungi. No death due to infection occurred in either group. However, the data of this study provide evidence that ITD is a more effective antimicrobial prophylaxis in bone marrow transplant recipients than SD.