In 5 paired studies, apheresis samples from the same mobilized cancer patient were processed in 3 aliquots to determine the more appropriate cell purification procedure for MP cell proliferation, evaluated as CFU-mega expansion. Cells were cultured in serum-free medium in the presence of MIP-1α, IL-3, IL-6, IL-11, FL, and MGDF, and SCF was added in 5 more paired studies. Results of LD cell culture were significantly inferior than those of CD34⁺ purified cells (P < .05, paired t-test). Among different methods for CD34⁺ cell enrichment, negative depletion of lineage-positive cells was associated with the generation of significantly larger quantities of clonogenic MP than enrichment based on positive selection (P < .05). Bar indicates 1 standard deviation. (□) LD cells; (▨) positive selection of CD34⁺ cells; (▥) lineage-positive cell depletion *P < .05 v LD cells. ^#P < .05 v positive selection.