Abstract: The drug-receptor interactions of dimethylcurine methylchloride (DMC) with toad rectus abdominis N₂-receptor were studied and compared with that of dtubocurarine chloride (d-TC). The antagonism of DMC to the ACh induced muscle contractions was completely overcome by increasing the concentration of ACh and the dose-cumulative-effect curves were parallel. The pA2 values of DMC and d-TC were 5.472 and 5.635 respectively. The K_B 's of DMC and d-TC were 0.363±0.011 (±SE) and 0.258±0.010 respectively. When the dose ratios log (X-1) were plotted versus negative log molar values of DMC (Schild plot), the regression slope was -0.96, very close to the theoretical value -1.0 of competitive antagonist. The calculated K_B's of different concentrations of DMC were approximately the same. These results strongly suggest that the DMC is a competitive antagonist and its affinity is about 70% that of d-TC on toad rectus abdominis.