Immuno-electron microscopy with the protein A-gold method demonstrated immunoreactive gold particles against 5-hydroxytryptamine localized in cored vesicles aggregating around presynaptic terminals of the gustatory cells in monkey and rabbit taste buds. The positive reactions were also found in the intragemmal and sub-epithelial nerve fibers. The role of these cored vesicles in taste transduction is still uncertain but the data strongly suggest that they may participate in a serotonergic modulation of a cholinergic synaptic transmission from the gustatory cells to the nerve endings.