AbstractThe variations of the glycoconjugate concentrations (PAS‐positive material), with special reference to the membrane sialic component have been studied during the annual cycle in erythrocytes of three mammalian species (Erinaceus europaeus, Glis glis, Talpa europaea) and of one amphibian species (Rana esculenta). InR. esculentathe structural modifications of nuclear chromatin (different degree of compactness) have also been examined through the propidium iodide intercalation at different concentrations.The membrane sialic components during hibernation increase inRana(457%),Glis(304%), andErinaceus(244%), and decrease inTalpa(59%), not really a hibernating species. These data can be related with a slowing down of erythropoiesis and with the increase of the average length of erythrocyte life in the winter. Residual glycoconjugate components are also modified with a similar, but less evident, pattern. The changes in the fluorescence fading during the annual cycle show a substantial independence from the concentration index of the PAS‐positive material; this fact might be related to molecular modifications or heterogeneity of the substrate.The DNA‐propidium iodide intercalation in frog erythrocyte chromatin decreases during the hibernation, possibly related to a reduced functional activity of