The mechanisms by which the fruit fly Drosophila melanogaster detects sweet compounds are poorly understood; however, a subset of the family of 68 gustatory receptors (Grs) has emerged as the key receptors. These seven transmembrane receptors include Gr5a and at least one member of the six genes in the Gr64 cluster (Gr64a), which are expressed in sugar-responsive neurons. Disruption of Gr5a prevents the detection of trehalose [1-3], whereas mutation of Gr64a impairs the responses to sucrose, maltose, and glucose [4, 5]. Recent studies suggest that these sugar receptors may require a coreceptor for function in vivo [4-6]; however, the identity of the putative coreceptor is not known. In the current work, we demonstrate that Gr64f is required in combination with Gr5a for the behavioral response to trehalose and for production of nerve responses to trehalose. Gr64f was also required in concert with Gr64a to rescue the defects in the sensitivities to sucrose, maltose, and glucose, resulting from deletion of the entire Gr64 cluster. These data suggest that Drosophila sugar receptors function as multimers and that Gr64f is required broadly as a coreceptor for the detection of sugars.