Taste buds are multicellular receptor organs embedded in the lingual epithelium of vertebrates. Taste cells within these buds are modified epithelial cells as they lack axons and turnover rapidly throughout life, yet have neuronal properties enabling them to transduce taste stimuli and transmit this information to the nervous system. Taste cells are heterogeneous, comprising types I, II, III and basal cells, and are continually replaced during adult life, raising the question of how these different cells are generated. The molecular mechanisms governing taste cell differentiation are unknown, but the Notch signaling system has been implicated in this process based upon recent gene expression data. Here we investigate the expression in mature taste buds of Notch related transcription factors, Hes6 and Mash1, which are among the first genes expressed in embryonic taste buds. We further compare these patterns with those of immunocytochemical markers of discrete taste cell types. We find that Hes6 is expressed in a subset of basally located, possibly progenitor cells, yet is rarely coexpressed with taste cell markers. In contrast, Mash1 is detected in some basal cells and in the majority of differentiated type III taste cells, but never in type II cells. These data suggest a role for Notch signaling in taste cell differentiation in adult taste buds.