The aim of this research was a comparative study of cyclic changes in secretory, destructive and proliferative processes in the adrenal cortex in dogs. Material and methods . Cyclic changes of morphofunctional indices of adrenal cortex in dogs (Canis familiaris) were studied. Healthy mature males were used. The material was collected in the period from December to April with a monthly interval. For light microscopy the fragments of the adrenal glands were fixed in Steve, Bouin and Zenker liquids, 10% neutral formalin solution. PAS-reaction was used. RNA was detected by the Brachet reaction and gallocyanine according to Einarsson. The material fixed in a 10% solution of neutral formalin was used to study lipids. Results. In January, in the adrenal cortex clearly expressed glomerular, fasciculate and reticulae zones. In the glomerular zone elongated cells with oval nuclei are situated, in the fascicular - polygonal cells with rounded nuclei. In February, a decrease in the functional activity of the cortical parenchyma and the development of extensive destructive changes in glandular cells, especially in the glomerular zone, were found in the adrenal cortex. In March, the development of recovery processes and increased secretory activity of the adrenal cortex were noted. Proliferative processes are accompanied by loosening of the capsule, the formation of connective tissue strands going into the fascicular zone. Among the fibers of connective tissue fibroblasts, fibrocytes and small poorly differentiated cells with rounded nuclei are disposed. These cells are converted into elongated cells of the glomerular zone and polygonal cells of the fascicular zone.