The number of CD34+ cells infused into patients at the time of autologous or allogeneic transplantation is a clinically important variable, but the viability of these cells has not been extensively documented. In this study, we analyzed the recovery of viable CD34+ cells before and after cryopreservation on 79 autologous stem cell products, using a novel flow cytometry assay without red cell lysis. For 70 PBSC harvest samples, the mean viable CD34+ cell count was 5.98 x 10(6)/kg (range 0.3-23 x 10(6)/kg) before freezing and 5.4 x 10(6)/kg (range 0.2-23 x 10(6)/kg) after thawing. The median recovery was 93% (range 48-107%), with 90% recovery for NHL (range 48-100%, n=34), 83% for multiple myeloma (range 56-106%, n=11), 92.3% for acute leukemia (range 71-100% n=7) and 94.5% for nonhematological malignancies (range 50-107% n=18). Similarly, for autologous bone marrows (n=9) the median recovery of viable CD34+ cells was 90% (range 68-100%). The recovery of viable CD34+ cells for adult (n=51) and pediatric (n=28) stem cell collections was 91 and 94%, respectively. Further examination of the correlation between the kinetics of hematological recovery and the number of viable progenitor cells infused, particularly at the lower end of the accepted dose range, may be warranted.