Summary Seventeen organic acids were used to evaluate the effect of (H+) concentration, total acid concentration, undissociated acid concentration, carbon chain length, polar groupings, and carbon to carbon double bonds on the stimulatory action of acids on human gustatory chemoreceptors. Parotid gland secretion rate was used to measure human response to the stimuli. Both hydrogen ion concentration and the chemical configuration of the anion were found to control the degree of response elicited.