We report our single institution's effort to standardize the method of collecting peripheral blood progenitor cells (PBPC) used for autologous transplantation. PBPC were mobilized by different types of chemotherapy followed by G-CSF (24 patients) or G-CSF alone (six patients) in 30 patients with various underlying neoplastic diseases. A median of three aphereses (range: 2-7), using the CS3000 cell separator was performed and a blood volume of 101 was processed. We studied the relationship between the absolute numbers of circulating leukocytes, mononuclear cells and CD34+ cells and the amount of PBPC collected during a single apheresis procedure. CD34+ cells were quantified by leukocyte subset analysis based on flow cytometry. Both CFU-GM and CD34+ cell contents of the apheresis products (69 procedures analyzed) correlated strongly: rho = 0.936, P = 0.0001). Regression analysis showed that the total number of CD34+ cells or CFU-GM content of the apheresis products could be predicted (r = 0.915, P = 0.0001) from the absolute number of CD34+ cells in the blood. A number of 10 circulating CD34+ cells per mm3 blood ensured a minimum of 0.5 x 10(6) CD34+ cells per kg, collected on the same day. Of the 30 patients, 17 received an autologous graft that contained only PBPC in 13. Long-term and complete hematological reconstitution was observed in all patients who had a minimum of 2 x 10(6) CD34+ cells per kg reinfused.