The axoplasmic transport of dopamine and opiate receptors in the striatonigral and nigrostriatal pathways was investigated by placing coronal knife cuts through these pathways and examining autoradiographically the accumulation of receptors at the site of the cut. In otherwise normal animals build-up of both receptors was found both rostral and caudal to the cut after a survival time of 24 h. Build-up of both receptors was reduced caudal to the cut by prior 6-hydroxydopamine lesions of the substantia nigra-ventral tegmental area, and reduced rostral to the cut by prior kainic acid lesions of the striatum. In addition, it was found by both autoradiographic and membrane binding methods that kainic acid lesions of the striatum produced a larger reduction of striatal opiate compared with dopamine receptors. The results suggest that opiate and dopamine receptors are axonally transported in fibers of both the nigrostriatal and striatonigral pathways possibly to their respective presynaptic terminals. The differential sensitivity of opiate and dopamine receptors in the striatum to local kainic acid lesions suggests the preferential localization of postsynaptic opiate receptors on dendritic trunks and neuronal somata, whereas the major localization of postsynaptic dopamine receptors may be on striatal dendritic spines, which to some extent appear to survive the lesions.