Aquatic organisms convert aromatic hydrocarbons into a variety of conjugated and nonconjugated derivatives. Analytical techniques based on thin-layer chromatography (TLC) and high-pressure liquid chromatography (HPLC) were employed to separate, identify and quantitate individual metabolites from fish exposed to radiolabeled naphthalene and 2,6-dimethylnaphthalene. Significant differences in profiles of individual metabolites were found in relation to the type of biological sample analyzed. Liver of naphthalene-exposed salmonids contained eight polar derivatives, as shown by HPLC. Two nonconjugates (1-naphthol and 1,2-dihydro-1,2-dihydroxynaphthalene) and three conjugates (1-naphthyl glucuronic acid, 1-naphthyl sulfate and 1-naphthyl glucoside) were identified. HPLC revealed that brain of 3H-naphthalene-exposed trout contained essentially the nonconjugated derivatives, 1-naphthol and 1,2-dihydro-1,2-dihydroxynaphthalene. TLC showed that the metabolites from trout urine were 1-naphthol, 1,2-dihydro-1,2-dihydroxynapthalene, and 1-naphthyl glucuronic acid (99% of the total metabolites detected). Major components of the metabolite fractions of tissues and biological fluids were 1,2-dihydro-1,2-dihydroxy and glucuronic acid derivatives. Dihydrodiol derivatives arise from the corresponding arene oxides, some of which have been shown to be cytotoxic to certain mammalian systems.