The influence of two different temperatures of cryopreservation of human bone marrow on the proliferative potential of granulocyto-monocytic (GM-CFU), erythroid (BFU-E) and megakaryocytic (CFU-Meg) progenitors was investigated. For this purpose, the human bone marrow cells were cryopreserved in the standard freezing medium supplemented with 10% DMSO and stored at -80 degrees C in a freezer or at -196 degrees C in a liquid nitrogen tank. Subsequently, cells were thawed, plated and stimulated in vitro to grow myeloid colonies. Unexpectedly, bone marrow cells stored at -80 degrees C formed about 60%, and those stored at -196 degrees C formed barely 8% of CFU-GM and BFU-E colonies respectively, in comparison to control non-frozen cells. CFU-Meg progenitors appeared to be the most sensitive to cryopreservation among all clonogeneic cells tested. The number of CFU-Meg derived colonies decreased to 20% in marrow cryopreserved at -80 degrees C and to about 2% in cells stored in liquid nitrogen at -196 degrees C. These data demonstrate the advantages of bone marrow storage at -80 degrees C over freezing in liquid nitrogen at -196 degrees C. Moreover, the increased sensitivity of CFU-Meg to cryopreservation could explain, at least partially, the clinical phenomenon of protracted thrombocytopenia observed in patients transplanted with the cryopreserved bone marrow cells.