This study identifies human and rat T1R receptors as key components of sweet and umami taste systems. The T1R family includes three members: T1R1, T1R2, and T1R3. Human T1R2/T1R3 recognizes a wide range of sweeteners, while human T1R1/T1R3 responds to umami stimuli like L-glutamate, with enhanced responses to 5'-ribonucleotides. These findings suggest that T1R subunits may form heterodimers for sweet and umami taste. The study also shows that T1R1/T1R3 may function as the sole umami taste receptor, as all tested umami stimuli require 5'-ribonucleotides for activation. However, discrepancies in rat T1R1/T1R3 responses to certain stimuli may reflect assay limitations or the involvement of other receptors. The study supports the hypothesis that mammalian T1Rs function as heterodimeric taste receptors, based on functional dependence, coexpression in taste cells, and structural similarities to the GABA type B receptor. The research highlights the importance of T1R subunits in taste perception and suggests that further studies on T1R-null mice could clarify their roles in taste.This study identifies human and rat T1R receptors as key components of sweet and umami taste systems. The T1R family includes three members: T1R1, T1R2, and T1R3. Human T1R2/T1R3 recognizes a wide range of sweeteners, while human T1R1/T1R3 responds to umami stimuli like L-glutamate, with enhanced responses to 5'-ribonucleotides. These findings suggest that T1R subunits may form heterodimers for sweet and umami taste. The study also shows that T1R1/T1R3 may function as the sole umami taste receptor, as all tested umami stimuli require 5'-ribonucleotides for activation. However, discrepancies in rat T1R1/T1R3 responses to certain stimuli may reflect assay limitations or the involvement of other receptors. The study supports the hypothesis that mammalian T1Rs function as heterodimeric taste receptors, based on functional dependence, coexpression in taste cells, and structural similarities to the GABA type B receptor. The research highlights the importance of T1R subunits in taste perception and suggests that further studies on T1R-null mice could clarify their roles in taste.