Electrophysiological and anatomical investigations of the olfactory epithelium of three salmonid species have been coordinated. Different corridors in the olfactory rosettes were examined by recording of the electro-olfactogram (EOG) using two recording electrodes simultaneously against one common indifferent electrode. Biopsies comprising the two lamellae bounding each of the examined corridors were examined by scanning electron microscopy (SEM). The electrophysiological results confirm a higher relative density of bile salt-receptors in the peripheral parts of all the corridors, and a higher relative density of amino acid-receptors in central parts. The SEM micrographs show that ciliated receptor cells are more numerous than microvillous ones. The density of ciliated receptor cells increases towards the peripheral margin of each lamella. The density of microvillous receptor cells increases towards the central margin. The correspondence between the electrophysiological and the anatomical observations support the hypothesis that the ciliated receptor cells are those specific to bile salt-like substances, the microvillous those specific to amino acids.