Seven continuous cell cultures were established from 45 lymphoid tissue specimens from 43 cancer patients. All cultures were free-floating and appeared to be primarily lymphoblasts. Electron microscopic examination revealed herpesvirus-like particles in all the established cell lines and in one cell line that was maintained for only 1 month. The particles appeared identical to those observed in Burkitt's lymphoma and other lymphoma and leukemia cultures. In one instance virus particles were observed in the original tissue specimen before cultivation. The virus particles were not infectious for several cell lines known to be susceptible to herpes simplex virus and other members of this group.