The purging efficacy of the Miltenyi sorting system was evaluated by qualitative and TaqMan quantitative polymerase chain reaction (PCR) in myeloma patients, using immunoglobulin genes. After small-scale selection, qualitative PCR showed that in 6 of 12 leukaphereses myeloma cells were no longer detectable. Envisaging a possible clinical application, the leukaphereses from three patients underwent large-scale selection. Qualitative PCR showed that myeloma cells were still detectable. Quantitative PCR, performed in two patients, showed a tumour depletion of 1 and 2 logs respectively. Although numbers are small, the promising results obtained with small-scale selection were not reproduced in large-scale experiments.