1. Sites of the cardioaccelerating action of nicotine, DMPP, McN-A-343, AHR-602, tyramine, angiotensin and neostigmine were investigated in spinal rabbits. 2. The cardioaccelerating action of the above substances was substantially weak in reserpine-pretreated rabbits. The accelerating action was scarcely observed after propranolol administration. 3. Tetrodotoxin and guanethidine did not affect the cardioacceleration due to nicotine, DMPP, tyramine and isoproterenol, but they markedly weakened that due to McN-A-343, AHR-602, angiotensin and neostigmine. 4. Chlorisondamine blocked the cardioacceleration by nicotine and DMPP; atropine that by McN-A-343 and AHR-602. 5. Appropriate doses of isoproterenol, nicotine, DMPP, McN-A-343, tyramine, angiotensin and neostigmine, when administered into the right auricle, produced almost the same degree of cadia acceleration as when they were given to the right ear vein. AHR-602 did not produce significant cardioacceleration through this route. 6. Nicotine, DMPP and neostigmine when injected into the right auricle produced marked cardioacceleration, whereas they produced little action when injected into the left ventricle. Isoproterenol and tyramine produced more marked effect by the intraauricular route than the intraventricular one. 7. McN-A-343, AHR-602 and angiotensin produced more marked cardioacceleration by the intraventricular administration than the intraauricular one. The intraventricular AHR-602 produced marked cardioacceleration. 8. It is inferred that the sites of cardioaccelerating action of nicotine, DMPP, and tyramine will be either the terminals of the adrenergic nerves or the extraneuronal stores of norepinephrine and that of McN-A-343, AHR-602, angiotensin and neostigmine will be the adrenergic neurons in the heart. The sites on which nicotine, DMPP, tyramine and neostigmine will act are chiefly distributed in the auricular tissues and those on which McN-A-343, AHR-602, and angiotensin act chiefly in the ventricular tissues.