Counterflow centrifugal elutriation (CCE) has been extensively employed in T cell depletion of bone marrow cells for allografting. Nevertheless very little is known about CCE properties of mobilized hematopoietic progenitors. In this study five leukapheresis products collected after chemotherapy and G-CSF from patients with non-Hodgkin's lymphoma were elutriated. Two mononuclear cell fractions were obtained containing smaller and less dense cells (lymphocyte fraction) and larger and denser cells (monocyte fraction), respectively. The presence of immature CD34+ progenitor cells, not co-expressing CD33, CD38 and HLA-DR antigens, was demonstrated in both cell fractions. CD34+ cells were isolated from each fraction and grown in various culture conditions (CFU-GM and BFU-E assay, blast cell colony assay, cytokine supplemented liquid culture). CD34+ cells isolated from the monocyte fraction showed a longer lasting expansion in liquid culture and a higher number of blast cell colonies than CD34+ cells selected from the lymphocyte fraction. Moreover a significant reduction of T cell number was obtained in the monocyte fraction. These data suggest that chemotherapy plus G-CSF-mobilized progenitor cells show a characteristic behavior when subjected to CCE, allowing an efficient T cell depletion without losing more immature progenitors.