Cells of origin of ascending nonprimary afferents to the dorsal column nuclei of rhesus monkeys have been identified in the spinal cord by the retrograde transport of horseradish peroxidase. These neurons are mainly located in lamina IV and medially in more ventral laminae of the dorsal horn on the side ipsilateral to the medullary injection. Large neurons in the ventral horn ("spinal border cells") also appear to project to the ipsilateral dorsal medulla. The dorsal column nuclei of a primate thus are the recipient not only of ascending dorsal root fibers but also of a more complexly integrated spinal input.