Use of the polymerase chain reaction to monitor the effectiveness of ex vivo tumor cell purging. The polymerase chain reaction (PCR) was used to detect residual malignant disease before and after ex vivo purging with monoclonal antibodies and complement or immunomagnetic treatment of BM samples contaminated with known numbers of t(14;18)-carrying tumor cells. Sensitivity of the PCR was demonstrated by detecting a specific t(14;18) amplification product in DNA extracted from a preparation consisting of one tumor cell among 10(5) normal cells. When BM contaminated with 1% to 5% t(14;18)-carrying cells from the B-cell lymphoma line SU-DHL-4 was subjected to two rounds of anti-B-cell pool of antibodies and complement (Ab-C) treatment a 3- to 4-log reduction of the pretreatment PCR signal was observed. A similar log-cell kill was detected using an independent clonogenic assay confirming the utility of the PCR approach. BM contaminated with a second B-cell lymphoma cell line, OCI-Ly8, was more resistant because a third cycle of Ab-C treatment was required to obtain a similar reduction in the PCR signal. A similar 4 logs of tumor cell removal was obtained using anti-B-cell antibodies conjugated to magnetic beads. These studies demonstrate that the t(14;18) PCR can be used to detect levels of tumor cells as low as 0.001%. This approach can be used to determine the effectiveness of BM purging in patients undergoing autologous BM transplantation as well as to assess the biologic role of minimal marrow disease. 