Morphofunctional properties of hemopoietic progenitor cells in victims of Chernobyl accident were investigated by the method of cultivating in gel diffusion chambers inserted into peritoneal cavity of experimental animals. The oppressing of colony-forming activity of CFU-GMdc (granulocyte-monocytic colony-forming units in diffusion chamber) in patients with ARS (acute radiation sickness) and recovery of those indices later testifies to the preservation and restoration of stem cells department during some period of time. No significant difference in colony-forming activity of bone marrow cells between control group and groups of people irradiated at different dose rates (from 0.25 to 0.5 Gy, from 0.5 to 0.75 Gy and from 0.75 to 1 Gy) was determined. However, depressing of efficiency and disturbance in differentiation in the colonies in some patients, predominance of eosinophilic colonies in majority of patients illustrate the need for a high degree of suspicion in establishing an early diagnosis. Early identification of these patients is important as they are at risk of eventual evolution into more hazardous clinical state.