Abstract: By means of liquid scintilation assay of ¹⁴C-compounds on paper technique, the metabolism of quaternary salt of ¹⁴C-Sinomenine A bis-Methyliodide, a muscle relaxant, was investigated.Two minutes after subcutaneous injection of the drug (6 mg/kg), the radioactivity was rapidly absorbed and distributed in tissues of mice. Maximum ¹⁴C-level was reached within 20 minutes after administration except in liver and gall blader in which ¹⁴C increased continuously to 101169 cpm and 156850 cpm at 90 minutes respectively. The radioactivity in the brain was found to be very low. ¹⁴C was found in the urine two minutes after drug administration and reached 387549 cpm in 90 minutes. The total amount of ¹⁴C excreted in urine within 90 minutes was 13% of the ¹⁴C administered.The maximun rate of ¹⁴C excretion in urine reached 15180 cpm within 10 minutes, and rapidly fell within 40 minutes and then dropped slowly afterwards.