Interaction between taste substances (i.e., taste qualities) was studied using a multichannel taste sensor with lipid membranes. It was revealed that four basic taste substances, sour, salty, bitter and sweet, mutually suppressed the increase in stimulation. Umami substances also caused suppression, but the mechanism of suppression differed to a large extent from those of the others; they markedly changed the response patterns of other taste substances. This result agrees with the neurophysiological and psychological views that umami is the fifth independent taste.