In the silver female eel (Anguilla anguilla L.) maintained in fresh water, surgical removal of Stannius corpuscles (SC) resulted in: a) A significant increase of wet weight of gill cells and the dry weight of gill filaments expressed as function of body weight. b) A proliferation and a hypertrophy of chloride cells shown by a significant rise of cell volume expressed as a precentage of the epithelial volume. c) An increase of the calcium (Ca) binding protein activity in the total branchial mucosa. These modifications are not observed when eels are maintained in Ca-free water. The results are discussed in relation to the Ca fluxes across gills in eels deprived of SC and gill morphological changes during sea water adaptation.