Intermediate-duration reversible neuromuscular blocking agents of the formula (I) ##STR1## where B and C are preferably para or may be meta and are each ##STR2## where W is CH.sub.2 or most preferably CH.dbd.CH R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same or different and are each hydrogen or lower alkoxy of 1 to 4 carbon atoms and preferably methoxy, Y is lower alkyl of 1 to 4 carbon atoms and preferably methyl, Z is hydrogen, lower alkyl of 1 to 4 carbon atoms, cyclopentyl, cyclohexyl, benzyl, or ##STR3## where ALKYL has 1 to 4 carbon atoms preferably where the O-ALKYL is at the 2, 3, 4 or 5 positions such as 4-methoxy benzyl and is most preferably 3,4-dimethoxy benzyl or 3, 4, 5-trimethoxybenzyl, n is 2, 3 or 4, most preferably 2 or 3 provided that at least one of R.sub.1 to R.sub.4 is lower alkoxy and most preferably where R.sub.1 and R.sub.4 is hydrogen and R.sub.2 and R.sub.3 are methoxy and X is a pharmaceutically acceptable anion.The neuromuscular blocking agents of formula I are useful for administration to a patient to cause skeletal muscle relaxation during surgery and are normally administered intravenously in a pharmaceutically acceptable carrier.