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Background Blood stem cells collected by apheresis are largely mononuclear cells in nature, so manipulation of blood stem-cell components freequently requires more time and reagents than for a marrow harvest. Reducing the nucleated cell number in mobilized blood stemcell collections, while preserving hematopoietic progenitor content, would make such manipulations simpler and less costly, but only if debulking procedures were not complex. Methods We evaluated separation of light-density cells and enrichment of CD34 + cells from mobilized peripheral blood stem-cell collections by density gradient centrifugation over buoyant density solution 60 (BDS 60) in a single, closed vessel. Results Fifteen apheresis products from five normal volunteers and eight cancer patients contained 3.44 (range, 1.19-5.51) × 10 10 nucleated cells. Following processing and washing, there was a median 29% recovery of nucleated cells, 79% recovery of CD34 + cells, 2.49-fold enrichment of CD34 + cells, 0.96-log depletion of CD3 + cells, 0.48-log depletion of CD56 + cells, and 0.72-log depletion of CD19 + cells. Results of processing were affected by the variability in composition of the apheresis products. The enrichment of CD34 + cells varied by donor type, and there was a logarithmic relationship between the preprocessing percentage of CD19 + cells and the log reduction in CD19 + cells. Recovery of cells after thawing and washing was acceptable for processed cells cryopreserved at concentrations over the range of 0.01-1.5 × 10 8 /mL. Discussion These results demonstrate a simple method by which an apheresis product of 1-5 × 10 10 cells can be debulked effectively in a single, closed vessel. [ABSTRACT FROM AUTHOR]