Nucleotides and amino acids are acknowledged categories of water-borne olfactory stimuli. In previous studies it has been shown that larvae of Xenopus laevis are able to sense amino acids. Here we report on the effect of ATP. First, ATP activates a subpopulation of cells in the OE. The ATP-sensitive subset of cells is almost perfectly disjoint from the subset of amino acid-activated cells. Both responses are not mediated by the well-described cAMP transduction pathway as the two subpopulations of cells do not overlap with a third, forskolin-activated subpopulation. We further show that in contrast to amino acids, which act as olfactory stimuli, ATP surprisingly activated a large number of sustentacular supporting cells, and to a much lower extent olfactory receptor neurons. The cells of the amino acid-and ATP-responding subsets featured differences in shape, size and position in the OE. The latencies to activation upon stimulus application differed markedly in these subsets. To obtain these results we used a novel dextran-TMR backfilled slice preparation of the OE. Furthermore we found out that an antibody to calnexin also labels SCs. [This work was supported by DFG:SFB 406 (B5) and by DFG Research Center for Molecular Physiology of the Brain (CMPB, Project B4)]