Centromedian-parafascicular (CM-Pf) complex of the thalamus receives inputs from the superior colliculus (SC). The CM-Pf neurons, in turn, project to the neostriatum. In order to establish a circuitry that the efferent terminals of SC neurons make direct synaptic contacts with thalamostriatal neurons in the CM-Pf complex, the anterograde tracer (biocytin) was injected into the unilateral SC and the retrograde tracer (wheat germ agglutinin conjugated to horseradish peroxidase, WGA-HRP) into the ipsilateral head of the caudate nucleus of the cat. The anterogradely labeled SC fibers and their terminals and retrogradely labeled CM-Pf neuronal elements were examined under light and electron microscope. At the light microscopic level, biocytin-labeled terminal-like varicosities were observed densely in the latero-dorsal part of the CM and the dorsal part of the Pf lateral to the fasciculus retroflexus. These varicosities were often in close proximity to HRP-labeled somata and dendrites of CM-Pf neurons. Electron microscopic analysis revealed that the biocytin-labeled synaptic boutons contained mainly round synaptic vesicles and established asymmetrical synaptic contacts with retrogradely labeled thalamostriatal neuronal elements, including perikarya, and small and large dendrites. In addition, anterogradely labeled terminals made synaptic contacts with unlabeled somata, small and large dendrites, and spines as well as profiles containing synaptic vesicles. These vesicle-containing profiles were considered to be pre-synaptic elements contacting on thalamostriatal neurons or the vesicle-containing dendrites of local circuit neurons. These results demonstrate that the neurons of the CM-Pf complex of the thalamus is involved in a di-synaptic tecto-striatal circuit.