This study demonstrates, for the first time, by both autoradiography and binding assay that [3H]Ro 15-1788 binds to carp brain with a high degree of anatomical selectivity. Saturation binding of the radioligand was determined in seven anatomically defined regions and suggested the presence of one class of binding sites (Type I-lke). In general, there was a good correlation between the autoradiographic and the binding data. By far, the optic tectum and the vagal, facial, and glossopharyngeal lobes showed the majority of [3H]Ro 15-1788 binding sites. Low to negative concentration of binding sites was detected in the cerebellum. The location of [3H]Ro 15-1788 binding sites in particular brain regions, indicates that benzodiazepine receptors could be associated with pathways involved in the control of basic central functions as spatial learning acquisition and retention, and feeding behaviour.