The gustatory system of mammals can sense four basic taste qualities, bitter, sweet, salty and sour, as well as umami, the taste of glutamate(1-6). Previous studies suggested that the detection of bitter and sweet tastants by taste receptor cells in the mouth is likely to involve G-protein-coupled receptors(2,7,8). Although two putative G-protein-coupled bitter/sweet taste receptors have been identified(9), the chemical diversity of bitter and sweet compounds leads one to expect that there is a larger number of different receptors(8,10,11). Here we report the identification of a family of candidate taste receptors (the TRBs) that are members of the G-protein-coupled receptor superfamily and that are specifically expressed by taste receptor cells. A cluster of genes encoding human TRBs is located adjacent to a Prp gene locus(12), which in mouse is tightly linked to the SOA genetic locus that is involved in detecting the bitter compound sucrose octaacetate(13-15). Another TRB gene is found on a human contig assigned to chromosome 5p15, the location of a genetic locus (PROP) that controls the detection of the bitter compound 6-n-propyl-2-thiouracil in humans(16,17).