Abstract: The potency of the blocking effects of dimethylcurine methylchloride (a derivative of an active principle from Cyclea hainanensis Merr) on the transmission of impulses through isolated rabbit supracervical ganglia was compared with that of d-tubocurarine. The relative potency of the former to that of the latter was 48.68%. As to the muscle relaxant effect on isolated rat phrenic nerve-diaphragm preparation, this valus was nearly the same (51.80%). The muscular relaxant effect of dimethylcurine methylchloride was shown to be antagonized by neostigmine and potassuim chloride and synergistic with d-tubocurarine. The results revealed that this drug might be classified as a nondepolarizing type of muscular relaxant and might possibly be used clinically as a substitute for d-tubocurarine.