Response of human bone marrow progenitor cells to X-rays in vitro

In 25 out of 33 cases the survival response of myeloid progenitor cells from fresh human bone marrows, X-irradiated in vitro in phosphate-buffered saline at 23 degrees C, was characterized by a two-term exponential relationship, with D0 values of 0.42 +/- 0.19 Gy and 1.38 +/- 0.37 Gy, respectively. In the remaining eight cases for which the colony-forming efficiency was 10 times lower, survival followed a single exponential function with D0 = 1.18 +/- 0.15 Gy. The biphasic response at 23 degrees C became a single exponential response when the temperature at irradiation was 30 or 37 degrees C.