Sucrose-quinine isohedons re 1, 4, 16, and 40% sucrose were determined for the rat. Isohedonic mixtures were located by the up-and-down method using a group of 24 Ss. An interaction was found between sucrose concentration and quinine hydrochloride concentration in their joint determination of the acceptability of sucrose-quinine mixtures. High levels of quinine always contributed negatively to the acceptability of mixtures. Low levels of quinine made positive contributions to acceptability but did so only when the component of the mixture was of high concentration. (15 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)