In ‘60 %’ aqueous dioxan containing perchloric acid, the rearrangement of 2-methoxyhydrazobenzene to 3-methoxybenzidine shows transitional kinetics. The apparent kinetic order in acid rises from 1·1 in 0·002N-acid to about 2·0 in 0·3N-acid, in a manner which agrees quantitatively with the idea that two independent mechanisms of rearrangement are under simultaneous observation.