Responses differed widely when rats were offered choices between water and solutions of GABA, its isomers alpha-aminobutyric acid (AABA) and alpha-aminoisobutyric acid (AIB), or of another 4-carbon amino acid, threonine. They preferred solutions of threonine and AABA starting at concentrations of about 30 mM; preference for threonine declined when its concentration was 330 mM or above. Rats never preferred GABA or AIB, but instead avoided these amino acids when concentrations were approximately 100 mM or above. Control rats showed strong preferences for drinking from a given location. Limited studies with humans showed variations in the concentrations at which they could detect GABA; the mean was about 0.06 mM, a concentration far below that at which rats began to avoid this amino acid. The ability of dietary GABA to depress food intake of rats (as shown in earlier studies) does not seem related to a uniquely high sensitivity to its gustatory qualities.