SummaryA study has been made of the cholinergic receptor induced by chronic denervation in the rat diaphragm. The agonists acetylcholine, carbachol and tetramethylammonium produced a dose‐dependent contraction of the denervated diaphragm. These agonists also brought about a graded depolarization of the muscle cells. Supramaximally effective doses of agonists caused desensitization of the preparation; however, there was no cross tachyphylaxis between acetylcholine and carbachol. An attempt to determine the dissociation constants of carbachol and tetramethylammonium from a comparison of equipotent doses was unsuccessful. (+)‐Tubocurarine and gallamine triethiodide antagonized the action of the agonists on the diaphragm. The logarithmic plot of dose ratio‐1 against tubocurarine concentration had the expected slope of close to unity. However, the logarithmic plot of dose ratio‐1 against gallamine concentration had a slope of less than unity; it is suggested that there may be competition between the quaternary nitrogens of gallamine for receptor anionic sites. Temperature changes between 21–35° did not significantly affect the dissociation constant (Keq) for tubocurarine or gallamine, suggesting a small or zero net enthalpy change for the binding reaction to the receptor, and a large positive net entropy term.