Oestradiol uptake by the brain and pituitary gland of the elasmobranch Scyliorhinus canicula, the lesser spotted dogfish, was investigated using the techniques of radioreceptor assay of cytosol and autoradiography. The autoradiographic study showed that the main areas of label concentration were the preoptic, habenular, and hypothalamic tuberal nuclei, and the ependyma of the third cerebral ventricle. Very little oestradiol uptake was detected in the pituitary lobes. The cytosol of the dogfish hypothalamus was found to contain oestradiol-specific receptors which also accepted diethyl stilboestrol (DES). These receptors, at 2°, had an average ligand affinity, as measured by the equilibrium dissociation constant (Kd), of 8.5 × 10-10 M and a saturation binding capacity (N) of 8.26 fM/mg supernatant protein. Similar binding affinities were found at 30° using the same tissue; the binding elements were found to be heat labile. Kd values were similar in all tissues sampled, but values of N were lower in the following tissues than in the hypothalamus: optic tectum (≤0.8 fM/mg supernatant protein); combined rostral median and neurointermediate pituitary lobes (RMNIL, ≤5.6 fM/mg supernatant protein); ventral pituitary lobe (≤0.47 fM/mg supernatant protein).