Urine was collected from four female rats for 3 days after two subcutaneous injections with 0.3 mg of 2-methyl[8-14C]naphthalene per kg. Of the 14C injected, 55% was found in the urine. The urine was solvent-fractionated into a toluene fraction (4.9% of urine 14C), a chloroform fraction (11.7%), two ethyl acetate fractions (41.7%), and a methanol fraction (37.8%). Only about 3-5% of urine 14C appeared to be unchanged 2-methylnaphthalene. A major radioactive peak which was isolated from the chloroform fraction was further subdivided into three peaks by HPLC. These metabolites, which may be three isomeric dihydrodiols of 2-methylnaphthalene, represented 6-8% of urine 14C. The more polar fractions contained several radioactive peaks when examined by TLC. One of these peaks was hydrolyzed with base to glycine and a 14C-labeled material which was similar to 2-naphthoic acid by TLC and by HPLC. Mass spectrometry of this latter material and of the unhydrolyzed metabolite confirmed the presence of 2-naphthoic acid and 2-naphthoylglycine, respectively. In total, 2-naphthoylglycine accounted for 30-35% of urine 14C.