Serotonin-immunoreactive fibers have been observed in the dorsal columns of the golden hamster spinal cord. The fibers were visualized using the PAP method which was intensified with a DAB-nickel substrate. The fibers were arranged preferentially in the mid-sagittal plane, and many were observed coursing from the dorsal columns into the dorsal gray matter. This serotonin-immunoreactive pathway may play a role in analgesia produced by dorsal column stimulation.