The authors describe the course of experimental trichosporosis in normal and X-irradiated ICR mice after i.v. inoculation with Trichosporon capitatum. The irradiated animals were considerably more sensitive to infection than normal animals. The LD50 challenge dose used was by approximately two orders lower (1 X 10(3) c.f.u. ml-1) in irradiated mice than in control animals. The histopathological examination of the internal organs of the infected mice demonstrated that the greatest tissue damage was associated with the kidneys, liver and spleen. However, the infectious agent was also found in heart, lungs and brain. The degree of impairment of the tissues was dependent on the inoculation dose and on the irradiation status. Miconazole (50 mg kg-1) was administered i.p. immediately after inoculation with Ts. capitatum and resulted in an alteration of infection and prolonged survival time. Miconazole was ineffective when challenge dose were used which produced 100% mortality (1 X 10(6) and 1 X 10(4) c.f.u. ml-1 for normal and irradiated mice, respectively). With the use of these doses also the course of infection was nearly identical both in the miconazole-treated and untreated animals.