The carcinogenic effects of two polycyclic aromatic hydrocarbons (PAHs), benzo(a)pyrene (BaP) and 7,12-dimethylbenz(a)anthracene (DMBA), were examined in the sheepshead minnow (Cyprinodon variegatus). Specimens 6 to 10 days old were exposed to aqueous PAH solutions for periods of 6 or 24 h once a week for one or two weeks. The bioassays included the following groups: (1) untreated control, (2) carrier (dimethylformamide) control, (3) low concentration (24-h BaP; 6-h DMBA) exposure, (4) intermediate concentration (24-h BaP; 6-h DMBA) exposure, (5) high concentration (6-h) exposure and, (6) high concentration (24-h) exposure. Concentrations of BaP measured by gas chromatography or fluorescence spectrophotometry were about 2 ppb (low exposure), 30 ppb (intermediate exposure), and 200 ppb (high exposure) and 1 ppb, 30 ppb, and 1200 ppb, respectively, for DMBA. Neoplastic lesions were not seen in control specimens from either test or in any of the BaP-exposed specimens. Exposure to the high DMBA concentration, however, induced hepatic neoplastic lesions in specimens from both the 6-h (38% incidence at 9 months) and the 24-h (36% incidence at 9 months) exposures. Extrahepatic neoplastic lesions were not found. Comparing the results of this study to those of other studies on the carcinogenic effects of waterborne PAHs on small fish species, we found that the sheepshead minnow was less sensitive than were the Japanese medaka (Oryzias latipes) or the guppy (Poecilia reticulata), both of which developed hepatic neoplasms after exposure to BaP and both hepatic and extrahepatic neoplasms after DMBA exposure.