An electron microscopic study of cytopathic tissue culture fibroblasts inoculated with material from an adult with a hematologic disorder was undertaken to characterize the agent or agents present. A Herpes‐type virus displaying similarities to the Davis strain of cytomegalovirus was observed. Mycoplasma was also identified by subculture. The early clinical course of this patient suggested chronic granulocytic leukemia. However, the Philadelphia chromosome was absent; the disease terminated in an aplastic state and no evidence of leukemia was detected at autopsy. Leukemoid reaction was the diagnosis by exclusion. An inciting organism was not identified. The Herpes‐type virus and other organisms isolated from this patient were considered opportunistic invaders. This study confirms previous findings of Herpes‐type virus in tissue cultures inoculated with urine of patients with leukemia and allied disorders. This virus resembles morphologically the particles observed in cultured Burkitt tumor, American lymphoma and leukemia cells.