The purpose of this study was to evaluate the correlation of preleukapheresis circulating CD34+ cells/muL, white blood cells (WBC), and platelet counts on the first day of apheresis with the yield of collected CD34+ cell counts in 40 patients with hematological malignancies (n = 29) and solid tumors (n = 11). The median numbers of apheresis cycles, numbers of CD34+ cells, peripheral blood (PB) mononuclear cells, and total nucleated cells collected were 2 (range, 1-4), 5.5 x 10(6) /kg (range, 0.05-33.78), 2.59 x 10(8)/kg (range, 0.04-20.68), and 7.36 x 10(8)/kg (range, 0.15-28.08), respectively. There was a strong correlation between the number of preleukapheresis circulating CD34+ cells/muL and the yield of collected CD34+ cells per kilogram (r = 0.962, p < 0.001). The threshold levels of PB CD34+ cell/muL to obtain greater than or equal to1 x 10(6)/kg and greater than or equal to2.5 x 10(6)/kg CD34+ cell in one collection were 12/muL and 34/muL, respectively. Fifteen of 17 (88%) patients who had greater than or equal to34 CD34+ cells/muL in the PB before collection reached the level of greater than or equal to2.5 x 10(6)/kg in a single apheresis. Despite a low r value, WBC and platelet counts on the first day of apheresis also correlated with the yield of collected daily CD34+ cells per kilogram (r = 0.482, p < 0.01 and r = 0.496 p < 0.01, respectively). These data suggest that preleukapheresis circulating CD34+ cells/muL correlated significantly better with the yield of collected CD34+ cells than WBC and platelet counts on the first day of apheresis. Using a value of 34/muL preleukapheresis circulating CD34+ cells as a guide for the timing of peripheral blood stem cells collections can be time saving and cost-effective.