The intrinsic AML-CFU sensitivity to cryopreservation was investigated. We compared the recovery of AML-CFU with six different freezing techniques in five myelocytic leukemic (AML) patients to the recovery of normal progenitors (CFU-GM and BFU-E) from control marrows. The recovery for AML-CFU (9.3% +/- 3.1, SE) was significantly lower (p less than 0.001) than for normal CFU-GM (48.4% +/- 4.6) and BFU-E (46.2% +/- 5.0). Moreover, the cloning efficiency of frozen AML-CFU was significantly reduced in 4/5 cases (p less than 0.001), as compared to fresh samples, while it was unaltered in 3/4 normal controls. There were no significant differences between the six freezing techniques, indicating that they are equally efficient for normal progenitors and inefficient for leukemic progenitors. These results indicate that human leukemic progenitors are more sensitive to cryopreservation than normal CFU-GM and BFU-E. These findings suggest that cryopreservation per se may have a purging effect in the context of autologous bone marrow transplantation for acute myelocytic leukemia in complete remission.