Changes in membrane electric potential in response to taste substances were studied for membranes containing differing amounts of negatively charged lipids in the membrane matrix of polyvinyl chloride and plasticizer. Responses to quinine showing bitterness decreased systematically with increasing the quantity of charged lipids contained in the membrane, whereas the response did not depend on differences in the hydrocarbon chains of lipids. The mechanism is discussed qualitatively in terms of hydrophobicity and hydrophilicity of the membranes.