Numerous reagents are used in the collection processing and storage of hematopoietic progenitor cells for transplantation. To decrease potential variations in the final component for transplantation, these reagents should be uniform in safety, potency, and efficacy. Pharmaceutical-grade reagents are ideal but often are not available. Recently, recombinant human deoxyribonuclease (DNase) was approved for the treatment of patients suffering from the pulmonary complications of cystic fibrosis. We tested this pharmaceutical for toxicity to hematopoietic progenitor cells. These cells were exposed to a range of incubation concentrations for both the recombinant enzyme and bovine DNase previously used in this laboratory. No loss of nucleated cells or hematopoietic progenitors was observed after short-term incubation (1 h) or with direct addition to the culture medium. No incremental toxicity was observed in using recombinant enzyme with murine anti-B cell antibodies and rabbit complement in an immunologic purge technique. A variable effect on cell recovery after thawing of cryopreserved bone marrow cells was observed for both enzyme sources. These data suggest that the pharmaceutical-grade, recombinant human DNase may substitute for previously used reagent-grade protein from animal sources.