Autoradiographic tracing methods were used to demonstrate a well-defined projection from the superior colliculus to the inferior olivary complex in the monkey. This projection originates within the deep layers of the superior colliculus, descends within the contralateral tecto-spinal tract, and terminates within the caudal 1/3 of the medial accessory nucleus. The terminal field is restricted to a densely packed, darkly stained group of cells located in the most dorsal segment of subnucleus b. In one animal, another group of olivary afferents was identified. These fibers also descend within the contralateral tecto-spinal tract, and terminate within the dorsal cap of Kooy. While it was not possible to determine the origin of this projection, our data suggest that it arises within a region adjacent to the rostral pole of the superior colliculus. The present study further indicates that in the monkey relatively few axons which course within the classical tecto-spinal tract pass caudal to the medulla.