One limitation of ASCT is the potential reinfusion of tumor cells contaminating PBSC. The Eligix B cell SC system consists of high-density microparticles coated with anti-B cell antibodies. To determine if this system eliminates B cells and lymphoma cells from PBSC, immunocytochemistry and PCR of the bcl-2/IgH rearrangement were performed, and correlated with patient outcome after ASCT. Eligible patients (n=29) had relapsed or transformed follicular NHL with bone marrow involvement <20%, and all lymph nodes <5 cm. PBSCs were mobilized with cyclophosphamide/G-CSF (n=21), and patients were conditioned with cyclophosphamide, carmustine and etoposide. Using immunocytochemistry on PBSC, the median number of CD20+ cells pre-purge was 310/10(6) (range 0-16692) and post-purge was 0.75/10(6); the median log B cell depletion was 2.7 (range 1.4-3.9). B cell depletion correlated with PFS after ASCT (P=0.06). Of 17 available samples for PCR, only four had a detectable t(14;18) breakpoint. After purging, all four remained PCR+; two had a 1-3 log depletion of lymphoma cells. At median follow-up of 18 months, 10 patients, including five infused with PCR-negative PBSC, have had disease progression. The paucity of PCR-informative patients, possibly related to in vivo rituximab therapy, limited the utility of minimal residual disease as a surrogate marker of clinical outcome.