Using the polymerase chain reaction (PCR) technique and total DNA extracts of Hodgkin's disease (HD)-involved lymph nodes, the t(14;18)(q32;q21) translocation was detected in 37 of 115 (32.2%) cases studied. No correlation was found between the presence of this translocation and bcl-2 protein expression in Hodgkin and Reed-Sternberg (HRS) cells detected by immunohistochemistry in 58 of 96 (60.4%) cases. To identify the cells carrying the t(14;18) translocation, single-cell DNA from HRS cells isolated by micromanipulation from frozen tissue sections of lymph nodes was investigated by PCR amplification. Eleven cases showing a positive band of the same size in at least two of five PCR experiments performed on the same total DNA extract were selected for single-cell PCR. We postulated that this repeated successful amplification could be indicative of the presence of the t(14;18) translocation in the neoplastic HRS cells. Single cells from frozen tumor sections of the t(14;18)-positive OCI LY8 cell line grafted into nude mice served as a positive control. The bcl-2/JH rearrangement, involved in this translocation, could be amplified from single-cell DNA of the latter tumor, whereas, in all of the HD cases, HRS cells were found to be negative. We conclude that the t(14;18) translocation is not localized in HRS cells, but in nonmalignant B bystander lymphocytes, admixed with these neoplastic cells.