The present study investigated the oxidative metabolism of 2-naphthyl isothiocyanate catalyzed by rat liver microsomes. Incubation of 2-naphthyl isothiocyanate, microsomes, and NADPH yielded either N,N'-di-2-naphthylurea or, on inclusion of 2-aminofluorene in the incubations, N-2-naphthyl-N'-2-fluorenylurea. These ureas were formed by the production of 2-naphthyl isocyanate, which reacted with its hydrolysis product, 2-aminonaphthalene, to yield the symmetrical urea or, with 2-aminofluorene, to form the mixed urea. Formation of N,N'-di-2-naphthylthiourea was also observed, since 2-aminonaphthalene reacted with the substrate. Urea formation was dependent on microsomes, NADPH, and O2. Use of microsomes from rats previously treated with Aroclor increased urea formation > or = 10-fold. The enzyme activity was inhibited by alpha-naphthoflavone, flavone, or CO and slightly inhibited by metyrapone, 7-ethoxycoumarin, or SKF-525A. It was not inhibited by methimazole or paraoxon. These data are consistent with a cytochrome P-450-dependent, oxidative desulfuration of the isothiocyanate to yield an isocyanate.