The present study examined whether modified xenobiotic transport, resulting from chlordecone (CD) or dieldrin pretreatment, would alter polycyclic aromatic hydrocarbon (PAH) or organochlorine (OC) target organ doses and subsequent tumor organospecificity or incidence rates in rainbow trout. Additionally, the potential for exposure to dieldrin or CD, following PAH exposure, to enhance tumor incidence was assessed. Evaluation of CD pretreatment effects on \[14C]CD disposition in trout was conducted following two ip (0-15 mg/kg) and two dietary (0-0.4 mg/kg/d) pretreatment regimes. To assess the influence of OC pretreatment on cancer induced by the PAH 7,12-dimethylbenz\[a]anthracene (DMBA), juvenile trout were fed control, CD (0.1, 0.4 mg/kg/d), or dieldrin (0.1, 0.3 mg/kg/d) diets for 9 wk, received a waterborne \[3H]DMBA exposure (1 mg/L, 20 h), and resumed control, CD, or dieldrin diets for 33 wk. \[3H]DMBA disposition and hepatic \[3H]DMBA binding were examined immediately and 24 h after exposure. Hepatic and stomach tumor incidences were determined 33 wk after DMBA exposure. CD pretreatment did not influence \[14C]CD or \[3H]DMBA hepatic concentrations, hepatic \[3H]DMBA DNA binding, or hepatic/stomach tumor incidence. It did, however, elevate bile \[14C]CD and \[3H]DMBA concentrations. Postinititation exposure to CD weakly enhanced DMBA-induced hepatic tumor incidence at the low but not the high CD dose. Dieldrin pretreatment did not influence stomach \[3H]DMBA equivalents or stomach tumor incidence but did cause an elevation in biliary and hepatic concentrations of \[3H]DMBA equivalents. \[3H]DMBA binding to liver DNA was significantly increased and hepatic tumor incidence was elevated by dieldrin pretreatment. Dieldrin treatment following DMBA initiation did not enhance hepatic or stomach tumor incidence. Ecoepidemiology studies, to date, have reported correlations between the co-occurrence of PAHs and OCs and elevated tumor incidence in feral fish, but cause-and-effect relationships have been difficult to establish. The results of the present study confirm that OCs, such as dieldrin and CD, play a role in modifying PAH-induced carcinogenesis in fish.