Previous studies have shown that deafferentation of the adult rat superior cervical ganglion results in a transient increase in levels of a 65 kDa synaptic vesicle membrane protein (SV). The present study indicates that the observed increase in SV after deafferentation is the result of new protein synthesis. Treatment with cycloheximide, a protein synthesis inhibitor, for 8 h at selected times after surgery produces decreases in SV which are greater than that observed after treatment of unoperated animals. The results suggest that an increased rate of synthesis of this protein is induced by deafferentation. Transsynaptic factors may play important roles in regulation of protein synthesis in sympathetic ganglia.