In basic medium arylthiols displace bromo and iodo groups activated by nitro substituents in 5(4)-halo-4(5)- nitroimidazoles . The bromo compounds are slightly more reactive than the iodo analogues. Substituents at C5 are more readily displaced than those at C4. Methylsulfonyl groups, similarly activated by an adjacent nitro substituent, are displaced by a variety of nucleophiles. The imidazolethiol products are readily oxidized to the sulfones.