We reviewed 333 concomitant blood and cytapheresis samples from 101 patients with solid malignancies of various histological cell types. All samples were analyzed for CFU-GM, BFU-E and CD34+ determination. We found a good correlation between progenitor assays CFU-GM and CD34+ determination in the blood and cytapheresis (r = 0.77, p < 0.0001 and r = 0.79, p < 0.0001 respectively). The number of CD34+ cells in the peripheral blood was predictive of the CD34+ yield in the cytapheresis (r = 0.86, p < 0.0001), and we determined that a threshold of 26 CD34+/microliter of blood was sufficient to harvest 10(6) CD34+/kg in a single apheresis. Thirty breast cancer patients received injections of peripheral blood stem cells after the same high-dose chemotherapy. For these patients, we found a significant correlation between the quantity of CD34+ cells or CFU-GM collected and both granulocyte and platelet recovery. In conclusion, there is a very good correlation between CFU-GM assays and CD34+ determination and a good correlation between circulating CD34+ cells and the yield obtained by the cytapheresis. The number of CD34+ cells collected is also significantly correlated with hematological recovery. Because CD34+ quantification is an accurate, fast and inexpensive technique, this can lead to the progressive forsaking of progenitor assays in a clinical setting.