138 patients with neutropenia (PMN's less than 1000), 66 of them with acute myelocytic leukaemia (AML), were hospitalised over a 6-year-period in reverse-barrier isolation. All had skin, orifices and gut decontamination. Fever occurred in 78% of the 216 neutropenic episodes. Overall, the incidence of septicemia during febrile episodes was 10% and the mortality from infection 7%; both figures were identical in the patients with AML and are lower than those normally found in this type of patients. Various factors that might be responsible for this low incidence of severe infections in neutropenic patients have been examined. The microbiological methods used to document infection were identical to those currently used. The severity of the underlying diseases and of neutropenia in the patients with AML was similar to that reported in other series. The measures taken for infection prevention, i.e. reverse-barrier isolation plus skin, orifices and gut decontamination, were not different than those used in many other centers, although their strict application in a small specialized unit might partially explain these favourable results. In addition the outcome of infection was analysed in relation to the response to treatment of the underlying disease. The mortality due to infection in patients with a tumor responding to chemotherapy was only 4% but was 45% in patients with end-stage malignant diseases. These results suggest therefore that infection in patients whose malignancy respond to treatment can be efficiently controlled by prompt empiric broad spectrum antibiotic therapy, and failures of antiinfectious treatment are mostly observed in patients with advanced cancer.