The potency and speed of onset of fazadinium and d-tubocurarine have been compared at three cumulative doses. Wtih thiopentone as the induction agent, the dose ratio fazadinium/d-tubocurarine ranged from 1.2 to 1.3 for single twitch reduction and from 1.1 to 1.2 for reduction of tetanus. The times taken for the development of 50% and 100% effect after each dose increment were not significantly different for the three doses of fazadinium and the 2nd and 3nd doses of d-tubocurarine. However, the 1st dose of d-tubocurarine was markedly slower than fazadinium to achieve a 50% and 100% effect.