2-8) thiazolium and benzothiazolium salts (plus bases) are used as catalysts for the benzoincondensation and it is found that catalytic activity depends strongly on the methylene bridge length. This result supports a previous postulation that bis (thiazolin-2-ylidene)s, and not thiazolin-2-ylidenes, are the catalyticspecies in the benzoincondensationcatalyzed by thiazolium salts plusbase.