The central connections between the superior cervical ganglion of the sympathetic trunk and the brainstem were investigated in five rats by trans-synaptic transport of lectin-conjugated horse-radish peroxidase. After injection of this tracer into the superior cervical ganglion, labelled cells were seen in both the ventral and dorsal parts of the medullary reticular formation. The neurons were found mainly on the same side as the injection site. Besides retrograde labelling, there was an antegrade termination within the nucleus of the solitary tract. We hypothesise that a nervous mechanism is involved in the pathogenesis of rheumatoid arthritis, and that a supraspinal input to the sympathetic ganglia might influence this mechanism.