Action of natural ribonucleotides on ATP receptors of rat nodose ganglion has been studied. Nucleotides containing guanine, uracil or hypoxanthine residues as nitrogen base are competitive blockers of the receptors. Their pharmacological activity decreases along with reduction of the polyphosphate chain length. The most efficient blocker among them is guanosine-5'-triphosphate. Cytidine nucleotides as well as adenine ones are agonists of ATP receptors, if their polyphosphate chain contains two or three phosphate residues and are blockers, if it contains only one residue.