Decrease of olfactory function in patients with Parkinson's disease (PD) has been reported by several authors. The current study investigated olfaction in PD patients using olfactory event-related potentials (OERPs) as an electrophysiologic correlate of olfactory function in combination with psychophysical testing. A specific focus was the influence of antiparkinsonian drugs. We investigated PD patients treated with antiparkinsonian drugs (n = 13) and PD patients who received no pharmacologic treatment (n = 18). They were compared to age-and sex-matched control subjects (n = 38). To obtain OERPs, stimulants were chosen to stimulate specifically the olfactory nerve (2.1 ppm vanillin, 0.8 ppm H2S). In addition, chemosomatosensory event-related potentials were recorded after trigeminal stimulation with 52% v/v CO2. Moreover, the subjects' ability to identify and to discriminate odorants was tested by means of a ''squeeze bottle'' technique. The study yielded the following major results: (1) Odor identification was impaired in PD patients. It was not influenced by treatment with antiparkinsonian drugs. (2) The OERP latencies were prolonged in both PD patients taking and not taking antiparkinsonian drugs; however, this effect was mare pronounced in PT) patients taking antiparkinsonian drugs. (3) The intranasal chemosensory trigeminal system seemingly was neither affected by the neuronal degeneration seen in PD nor by treatment with antiparkinsonian drugs.