Betel chewing in man often produces palpitations, sweating, facial flushing and a warm sensation in the body. These observations suggest that betel chewing may affect the autonomic nervous system. To examine this, the RR interval variation (RRIV) was studied to determine if betel chewing might affect parasympathetic function. Three experimental groups of people consumed a betel nut preparation, betel quid and chewing gum, respectively. Recordings of RRIV were made before and during chewing. When one or two betel nut preparations were consumed, the main effect was a cardioacceleratory response. With increasing consumption of betel nut preparation, there was a reduction in RRIV, particularly during deep breathing. Consumption of betel quid or chewing gum had no effect on RRIV. The effect of betel chewing was dose-dependent. Consumption of a small amount caused cardioacceleratory response suggesting a sympathetic activation, while consumption of a large amount reduced RRIV, suggesting involvement of the parasympathetic function.