By administration of p-chlorophenylalanine (PCPA), a synthetic inhibitor of 5-hydroxytryptamine (5-HT), to rabbits, granular vesicles in the taste receptor cells remarkably decreased their contents. The recovery of this core substance depletion occurred in specimens killed on the 15th day after injection of the drug and in animals injected with 5-hydroxytryptophan (5-HTP) after treatment with PCPA. Electron microscope observation suggests that granular vesicles in the receptor cells are 5-HT-storing particles and favors the view based on recent fluorescence histochemistry which indicates the presence of a biogenic monoamine, presumably 5-HT, in rabbit foliate taste bud cells.