We have investigated the structure and the cholinesterase features of the brain capillaries in two adult Amphibians (Rana esculenta and Bufo bufo). We found that brain capillaries are un-fenestrated and the endothelial cell edges are joined by tight junctions. The brain capillaries in both species are characterized by high levels of AChE. This enzyme is only localized in the basal membrane, whereas we have found the reaction product neither in the endoplasmatic reticulum nor in the Golgi apparatus. On the contrary the brain capillaries are deprived of BuChE. Only in one experiment traces of reaction product were found. The significance of this datum and the non-nervous role of cholinesterase is discussed.