Better discrimination was possible between threshold PTC solutions and pure solvent when the solvent was a tasteless, low concentration NaCl solution to which the subject had adapted, than when the solvent was purified water. The reverse was true for threshold NaCl stimuli. Subjective reports indicated this to be due to the absence or presence of taste cues from the solvent and stimulus after-effects. Interstimulus rinsing with the appropriate solvent improved discrimination.