Nevirapine (NVP) treatment is associated with a significant incidence of skin rash in humans, and it also causes a similar immune-mediated skin rash in Brown Norway (BN) rats. We have shown that the sulfate of a major oxidative metabolite, 12-OH-NVP, covalently binds in the skin. The fact that the sulfate metabolite is responsible for covalent binding in the skin does not prove that it is responsible for the rash. We used various inhibitors of sulfation to test whether this reactive sulfate is responsible for the skin rash. Salicylamide (SA), which depletes 3'-phosphoadenosine-5'-phosphosulfate (PAPS) in the liver, significantly decreased 12-OH-NVP sulfate in the blood, but it did not prevent covalent binding in the skin or the rash. Topical application of 1-phenyl-1-hexanol, a sulfotransferase inhibitor, prevented covalent binding in the skin as well as the rash, but only where it was applied. In vitro incubations of 12-OH-NVP with PAPS and cytosolic fractions from the skin of rats or from human skin also led to covalent binding that was inhibited by 1-phenyl-1-hexanol. Incubation of 12-OH-NVP with PAPS and sulfotransferase 1A1*1, a human isoform that is present in the skin, also led to covalent binding, and this binding was also inhibited by 1-phenyl-1-hexanol. We conclude that salicylamide did not deplete PAPS in the skin and was unable to prevent covalent binding or the rash, while topical 1-phenyl-1-hexanol inhibited sulfation of 12-OH-NVP in the skin and did prevent covalent binding and the rash. These results provide definitive evidence that 12-OH-NVP sulfate formed in skin is responsible for NVP-induced skin rashes. Sulfotransferase is one of the few metabolic enzymes with significant activity in the skin, and it may be responsible for the bioactivation of other drugs that cause skin rashes.