In a cohort of 79 febrile episodes in 50 consecutive neutropenic patients seen at the University Hospital, Federal University of Rio de Janeiro, Brazil, between 1987 and 1991, it was observed that the cumulative incidence of disseminated fungal infections rose from 3% to 19% after the introduction of a new empirical antibiotic regimen. In order to identify risk factors, as well as to assess the impact of the new antibiotic regimen on the emergence of fungal infections, a nested case-control study was undertaken, in which 10 cases of disseminated fungal infections were compared with 30 randomly chosen controls, drawn from the same cohort. In a multiple logistic regression analysis, the predictive factors for disseminated fungal infection were younger age (odds ratio 0.85, 95% confidence interval 0.75-0.97) and use of the new antibiotic regimen (odds ratio 14.18, 95% confidence interval 1.05-191.80) The probable explanation for the emergence of fungal infections is that the new antibiotic regimen, by lowering the incidence of bacteraemia-related deaths, allowed patients to be at risk for the development of disseminated fungal infections.