Five patients with lethal disseminated toxoplasmosis have been seen within a two-year period at the Swedish Hospital Medical Center and the University of Washington Hospital. In all patients, there was a severe underlying disease treated with various chemotherapeutic agents, corticosteroids, splenectomy, or irradiation. Although the clinical presentations were variable and masked by the underlying illness, therapeutic measures, or concomitant infectious processes, or both, the autopsy findings were strikingly uniform in that the brain, myocardium, and lungs were invariably affected. Reports in the literature and our experience indicate that disseminated toxoplasmosis in compromised hosts is being recognized with increasing frequency.