A survey for HBLV (human B-lymphotropic herpesvirus or human herpesvirus 6) sequences by Southern blot analyses was performed on DNA obtained from a variety of pathologically defined tissues, including a number of lymphomas, leukemias, and tissues from other hematologic disorders. Of the over 50 specimens studied, viral sequences were detected in three lymphomas of B cell derivation: an Epstein-Barr virus-positive African Burkitt's lymphoma, a follicular large cell lymphoma (nodular histocytic lymphoma), and two Epstein-Barr virus-negative tumors from a patient with Sjogren's syndrome. These results are the first indication of HBLV sequences associated with B cell tumors in a limited number of cases and raise the possibility that the virus might be involved in the genesis of some B cell tumors.