Successful engraftment of autologous bone marrow depends on preserving the viability of stem cells during cryopreservation. While several techniques for effective bone marrow and peripheral blood stem cell collection and processing have been reported, little is known about the effect of the duration of cryopreservation on stem cell viability in humans. We reviewed, retrospectively, the engraftment data of 33 patients with leukemia treated at Brigham and Women's Hospital, Boston and the European Bone Marrow Transplant Group from 1981-1989 who received stem cells cryopreserved for greater than or equal to 2 years. Data on cryopreservation methods are available in 18 of 33 patients. In all cases, stem cells were frozen in liquid nitrogen with a programmed freezer and stored at or below -140 degrees C. The median duration of cryopreservation was 2.8 years (range 2-11 years). Thirty of 32 (94%) evaluable patients achieved granulocyte counts greater than 500 x 10(6)/l (median 23 days; range 10-119 days); 26 of 32 (74%) evaluable patients achieved platelets greater than 50 x 10(9)/l (median 30 days; range 19-128 days) while 22/32 (69%) patients achieved platelets greater than 100 x 10(9)/l (median 45 days; range 20-328 days). This report demonstrates that human stem cells cryopreserved for up to 11 years are capable of engrafting. Stem cells may be stored for prolonged periods and used for transplantation in patients harvested prior to pelvic irradiation or alkylating agent therapy.