In mice, aversion to the bitter acetylated sugar sucrose octaacetate (SOA) is determined by a single genetic locus with three alleles. SWR/J (SW) inbred mice are SOA tasters: They avoid many compounds characterized as bitter-tasting by humans, at concentrations to which C3HeB/FeJ (C3:SOA demitasters) mice are less sensitive. C3.SW-Soa(a) congenic taster mice contain the taster allele transposed to a 99% C3 bitter-insensitive genetic background. SW, C3, C3.SW-Soa(a) congenic taster, and C3.SW demitaster mice were behaviorally tested with a series of 48-h two-bottle preference tests to determine the influence of the Soa(a) taster allele on sensitivity to a variety of bitter-tasting compounds. Soa allelic variation had a major effect on sensitivity to 0.003-1.0 mM SOA and several concentrations of the bitter-tasting alkaloids brucine, strychnine, and quinine. Effects were also found for 0.1 mM denatonium and 1 mM propylthiouracil. For caffeine, cycloheximide, thiamine, and two nonbitter compounds (NaCl and calcium hydroxide), the SW mice avoided lower concentrations than the other strains, but this avoidance was not due to the Soa(a) allele because both the C3 inbred and C3.SW-Soa(a) congenics were less sensitive. These results suggest the Soa gene product influences sensitivity to a subset of bitter-tasting compounds.