Chemosensory function is determined by the interplay of numerous sensory modalities. The present study aimed to evaluate the possible influence of electrical stimulation of the left-sided vagal nerve on gustatory and olfactory function in patients with vagal nerve stimulation (VNS). Gustation and olfaction were tested using psychophysical techniques; olfactory function was additionally evaluated using event-related potentials. A total of 11 subjects participated (six men and five women, aged 21 to 56 years). The vagal stimulator was run in "rapid cycle mode" in 10 patients, whereas one patient was treated with "normal mode" VNS. Subjects participated in two sessions, with the vagal stimulator switched on and off, respectively. The sequence of the two sessions was randomized across all participants. Using air-dilution, olfactometry event-related potentials to the specific olfactory stimulant H₂S were recorded. Psychophysical tests were performed using the "Sniffin' Sticks" test kit, a test for retronasal olfactory function, and a gustatory test based on impregnated filter paper. The study yielded the following major results: (1) VNS produced a prolongation of P2 latencies of olfactory ERP, and (2) patients with therapeutic benefit from VNS in terms of seizure control had larger amplitudes during the on period than during the off period. In conclusion, using electrophysiological measures of olfactory function, the present study indicated a significant role of VNS in the processing of olfactory information.