Life-threatening disseminated infection with Trichosporon beigelii (trichosporonosis) is a rare mycosis most commonly seen in patients with hematologic malignancies made neutropenic by cytotoxic therapy. This infection is usually resistant to conventional antifungal therapies. Poor correlation between therapeutic outcome of trichosporonosis and in vitro susceptibility of clinical isolates of T. beigelii to antifungal agents is often reported. To obtain a better understanding of its pathogenesis, and to aid in the future study of the therapy of this disease, a murine model of trichosporonosis was developed. The in vitro growth of clinical isolates of T. beigelii was first studied. Subsequently, mice made neutropenic with cyclophosphamide were inoculated intravenously with the fungus to produce the disease model. Inoculum size which produced 100% mortality, yet allowed an apparent therapeutic window (6 x 10(6)) was determined. Tissue distribution and burden of organism during the course of infection was examined by viability and histopathologic studies. T. beigelii disseminated rapidly in this model, involving numerous organs including the heart, brain, kidneys, lungs, and liver. The heart and kidneys of the infected animals showed evidence of infection as early as 6 hours following inoculation. Further understanding of the pathogenesis of trichosporonosis in the neutropenic host was imparted by this study. This will aid in the future study of antibiotic treatment of this disease and its untreated progression.