2-Aminothiazole condensed with acetsulphanilylchloride in aqueous solution or suspension in the presence of sodium bicarbonate, calcium carbonate or barium carbonate to yield 2-diacetsulphanilylamidothiazole m.p. 128–29°; the same product is also obtained by condensing 2-aminothiazole with two molecular equivalents of acetsulphanilylchloride in pyridine or by condensing 2-acetsulphanilamidothiazole with acetsulphanilylchloride in alkaline solution. This compound on boiling with alcohol isomerises into 2-acetsulphanilimido-3-sulphanilylthiazolone. These two products are hydrolysed by acid or alkali to sulphathiazole in good yield. A process of preparation of sulphathiazole is described.