Clinical data from 10 episodes of disseminated infection with Fusarium among eight recipients of bone marrow transplants and from 31 cases reported previously in the literature were analyzed in an effort to characterize the natural history of this rare infection and its response to therapy. The characteristic signs of fusarial infection--disseminated skin nodules, fungemia, and multiple-organ involvement--are results of its propensity for early spread. From a review of the literature and our own experience, it appears that recovery of phagocytic mechanisms (the primary immunologic defenses against Fusarium) in the form of rising neutrophil counts is mandatory for clinical resolution. Even after a graft begins to function adequately, Fusarium may not be completely eradicated, as evidenced by the high incidence of recurrence among patients with subsequent neutropenic episodes. Fusarium is highly resistant to conventional antifungal drugs in vitro, but its progression may be slowed by intensive antifungal therapy until the recovery of adequate neutrophil levels.