PTC and PROP behave differently in tests of discrimination from their solvents.

Better discrimination was possible between phenylthiocarbamide (PTC) solutions and the 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 6-n-propylthiouracil (PROP). The differences in discrimination for PROP and PTC in the different solvents were caused by differences in the intensity and persistence of aftertastes, rather than a more intense perception of the PTC and PROP tastes per se. This has consequences for traditional approaches to measuring taste sensitivity, as well as indicating that PTC and PROP are not necessarily equivalent indicators of 'taster' versus 'non-taster' status.