Object of the investigation were effects of elevated radiation background on specific body systems in two generations of rats that had been chronically exposed to radiation in the most badly polluted areas of the Kaluga district and eaten local food. Findings included some compensatory deviations in the white blood count, decrease in karyocytes and increase in chromosomal aberration rate in nucleus-containing cells from the femoral bone marrow in younger animals of several groups, morphologic and histochemical shifts in mucous membrane of the esophagus and the stomach, and morphofunctional changes in neurons and glia of the cerebral cortex. These changes are compensatory-adaptive by nature and indicative of destabilization of homeostasis in experimental animals.