1. The pattern of conjugation in the ferret of 8 arylacetic acids and, for comparison, benzoic acid and 4-nitrobenzoic acid was examined.2. The arylacetic acids, phenylacetic, 4-chloro- and 4-nitro-phenylacetic,α-methylphenylacetic (hydratropic), 1- and 2-naphthylacetic and indol-3-ylacetic acids, were excreted in the urine as taurine and glycine conjugates. Diphenylacetic acid did not form an amino acid conjugate and was excreted as a glucuronide.3. The taurine conjugate was the major metabolite of 4-nitrophenylacetic,α-methylphenylacetic, 1- and 2-naphthylacetic and indol-3-ylacetic acids, whereas the glycine conjugate was the major metabolite of phenylacetic and 4-chlorophenylacetic acids. Taurine conjugation did not occur with benzoic and 4-nitrobenzoic acids which were excreted as glycine and glucuronic acid conjugates.4. Phenacetylglutamine and 4-hydroxyphenylacetic acid were minor urinary metabolites of phenylacetic in the ferret.5. A number of taurine conjugates of aliphatic and aromatic acids were synthesized and their characterization and properties were studied. The role of taurine as an alternative to glycine in the metabolic conjugation of arylacetic acids is discussed.