In a neutral aqueous solution of (phenylthio)acetic acid, the hydroxyl radical is observed to react with a bimolecular rate constant of 7.2 x 10(9) dm(3) mol(-1) s(-1), and the transient absorption bands are assigned to (OH)-O-. radical addition to benzene and sulfur with rough estimated values of 50 and 40%, respectively. The reaction of the (OH)-O-. radical with diphenyl sulfide (k = 4.3 x 10(8) dm(3) mol(-1) s(-1)) is observed to take place with the formation of the solute radical cation, OH-adduct at sulfur, and benzene with rough estimated values of 12, 28, and 60%, respectively. The transient absorption bands observed on reaction of the (OH)-O-. radical, in neutral aqueous solution of 4-(methylthio)phenyl acetic acid, are assigned to solute radical cation (lambda(max) = 550 and 730 nm), OH-adduct at sulfur (lambda(max) = 360 nm), and addition at benzene (lambda(max) = 320 nm). The fraction of (OH)-O-. radical reacting to form a solute radical cation is observed to increase with increasing concentration of acid, and in highly acidic solutions, the solute radical cation is the only transient species formed on reaction of (OH)-O-. radical with these sulfides.