The effect of unilateral 6-hydroxydopamine lesions of the medial forebrain bundle on the specific binding of [125I]iodosulpride and [125I]SCH 23982 in the rat substantia nigra was determined by quantitative autoradiography of adjacent sections. The specific binding of [125I]iodosulpride was reduced by 40-70% on the lesioned side in the substantia nigra pars compacta, reticulata, lateralis and in the ventral tegmental area. In contrast, the specific [125I]SCH 23982 binding was unchanged in all subdivisions of the substantia nigra. The results indicate that dopamine autoreceptors are present in the substantia nigra and in the ventral tegmental area and that they are exclusively of the D2 type.