Résumé : In vitro uptake and binding of tritiated estradiol to the specific granules of eosinophil granulocytes has been observed by ultrastructural radioautography in various tissues of the rat (liver and spleen of newborn, small intestine and bone marrow of adult animals). Binding of 3H-estradiol to granules present in the cytoplasm of neutrophil granulocytes has also been observed in bone marrow and in a cholangioma produced by chemical carcinogenesis. Neither type of granulocyte bound 3H-testosterone. © 1977 Springer-Verlag.