Among the factors which enable successful bone marrow transplantation, the ability to store and subsequently recover sufficient viable marrow cells to reestablish hematopoiesis is crucial. In most centers, marrow is typically prepared for long term storage by programmed, controlled rate freezing with subsequent placement into the vapor phase of liquid nitrogen. Though clearly effective, this procedure is time consuming and equipment intensive. Since cost containment is an important issue for all medical procedures, we evaluated the utility of a faster and less costly method to accomplish the same purpose. We found that when CD34+ bone marrow cells are immediately frozen and stored at -80 degrees C, the number and quality of stem/progenitor cells recovered after thawing was comparable to those reported recovered after conventional processing. Herein we report optimized conditions for cryopreserving and storing CD34+ bone marrow cells at -80 degrees C and for subsequent thawing of the stored product. With these methods post-thaw recovery of CFU-Mix, for example, equaled or exceeded 80% of predicted numbers, even after six months of storage. Further, though progenitor cell recovery does not necessarily correlate with speed of engraftment, these results nonetheless suggest that storage of human CD34+ cells at -80 degrees C in a mechanical freezer is a convenient, inexpensive, and reliable method for storing marrow for transplantation.