When substances of similar taste are mixed, the mixture can show suppression or synergism. That is, the perceived intensity of the mixture can be less than or greater than the sum of the perceived intensities of the components. In the present study, these departures from simple additivity could be predicted from the psychophysical functions relating tast intensity to stimulus concentration of the unmixed components. Psychophysical functions are said to show compression when successive increments in concentration produce progessively smaller increments in perceived intensity and to show expansion when successive increments in concentration produce progressively larger increments in perceived intensity. Suppression resulted from mixtures of substances with compressed psychophysical functions, and synergism resulted from mixtures of substances with expanded functions.