Journal of Virological Methods, 21 (1988) 191- 197 Elsevier 191 JVM 00774 Polymerase chain reaction amplification and in situ hybridization for the detection of human B- lymphotropic virus A. Buchbinder’, S.F. Josephs’, D. Ablashi’, S.Z. Salahuddin’, M.E. Klotman’, M. Manak”, G.R.F. Krueger”, F. Wong-Staal’ and R.C. Gallo’ lLaboratory of Tumor Cell Biology, and ‘Laboratory of Cellular and Molecular Biology, National Cancer Institute. Bethesda, M ary land, U.S.A., ‘Biotech Research Inc., Rockville. Maryland. U.S.A. and ‘Institute of Pathology, University of Cologne, Cologtte, F. R. G. Summary Polymerase chain reaction amplification (PCR) is a recently described technique that allows for the amplification of a given sequence of DNA. It can be used to reliably amplify sequences of up to 3 kb within hours. The amplified sequence can then be recognized by hybridization with a specific probe after transfer onto ni- trocellulose or nylon paper. We used PCR to recognize human B-lymphotropic vi- rus (HBLV or HHV-6) specific sequences in various tumors as well as in the blood of patients with AIDS. Sixty-three specimens of DNA extracted from peripheral blood of patients with AIDS as well as DNA extracted from various lymphopro- liferative disorders were analysed; 52 out of 63 (S3%) patients with AIDS were found to have amplification of the HHV-6 specific sequence; 2 out of the 63 (3%) had equivocal amplification and 9 (14Y ) o were found to be negative. Twenty out of 23 tumors were found to have amplified HBLV-specific sequences. Only one of these tumors was positive by Southern hybridization on restriction enzyme di- gested genomic DNA. In situ hybridization of clinical specimens using radiolabelled RNA probes or hapten-labelled DNA probes was used to detect the presence of HBLV in tumors. Three tumors of B cell origin were found to be positive for HBLV. HBLV; PCR; AIDS; Human tumor Correspondence to: A. Buchbinder. Laboratory of Tumor Cell Biology, National Cancer Institute, Be- thesda, MD 20892. U.S.A.