Objective: to investigate the erythron and hematological reactions in miners in relation to the length of underground work. Subjects and methods. A prospective study of peripheral blood red cell parameters was conducted in 482 miners with an underground work length of as long as 40 years, who were divided into 3 length groups. Age subgroups were identified from the length groups to define the significance of age-related changes. A control group comprised 30 apparently healthy volunteers who did not work under harmful working conditions. Results and discussion. The miners were found to have the following statistically significant changes in red blood cell parameters in relation to the underground work length: elevated levels of red blood cells and hemoglobin as their adaptation to chronic hypoxia and intoxication in the first 10 years of underground work, which were more pronounced in young people (aged less than 29 years), this results from the accelerated release of red blood cells from the bone marrow into the bloodstream. Thereafter, there is a satisfactory adaptation or resistance phase that makes itself evident in the stabilization of erythron parameters. This process is accompanied by the change in the morphophysiological parameters of red blood cells themselves, which may present as increases in average hemoglobin concentration in the red blood cells and in their average hemoglobin volume. The alteration of cell volume is associated with the longer maturation of red blood cells and their increased hemoglobin volume. Conclusion. Our investigation has established that that the miners with an underground work length of less than 10 years, exposed to intermittent hypoxia and intoxicated with coal-ore dust, show a compensatory rise in red blood cells and hemoglobin levels; those with a length of 10 years or more had exhausted adaptive resources, as shown by the downward trend for red blood cells and hemoglobin, which is compensated for by increases in the volume of red blood cells and their hemoglobin concentration. Keywords: hypoxia, red blood cells ta^gbWn general adaptation syndrome.