Using a sensitive, radioisotopic assay for aryl hydrocarbon hydroxylase (AHH), a comparatively low level of benzo(a)pyrene (BaP) metabolism was routinely measured in digestive gland homogenates. Attempts to induce overall BaP metabolism by exposure to Aroclor 1254, an inducer of mammalian AHH, were largely unsuccessful. However, Aroclor treatment produced an altered BaP metabolite profile for each bivalve species tested. The metabolites were separated and identified by coelution with authentic standards, using high-performance liquid chromatography. Untreated mollusks produced several dihydrodiols and phenolic derivatives; Aroclor treatment usually resulted in augmented generation of 9, 10-, 4,5-, and 7,8-diols, as well as production of quinones and atypical monohydroxylated metabolites. The data suggest that BaP biotransformation by bivalve enzyme systems can yield both potentially carcinogenic (BaP 7,8-diol) and detoxified metabolites. However, no apparent activation of BaP by molluscan enzymes was seen using the Ames Salmonella tester strains.