Juvenile pink salmon Oncorhynchus gorbuscha were exposed for 40 days to stable, sublethal concentrations of naphthalene (<0.80 mg/liter) and the water-soluble fraction of Cook Inlet crude oil (<0.87 mg/liter total aromatic hydrocarbons). All fish were fed equal daily rations of Oregon Moist Pellet Formula II. Concentrations (percentage of the 96-hour LC50, median lethal concentration) of 10% naphthalene and 14% water-soluble fraction of crude oil did not affect wet weight or length of exposed fish. At higher concentrations, however, growth per day determined from wet weight decreased with increased toxicant concentration. Change in length of the fish was not a sensitive measure of toxicity. Fish exposed for 40 days to concentrations of toxicants as low as 33% of the 96-hour LC50 weighed significantly less than control fish (P < 0.05). Juveniles exposed to the water-soluble fraction of crude oil had slower growth rates than those exposed to the same concentration (percentage of the LC50) of naphthalene. Fish exposed to either naphthalene or the water-soluble fraction of crude oil had decreased caloric content; however, fat content of the fish was not affected. Chronic marine oil pollution at a concentration as low as 0.40 mg/liter total aromatic hydrocarbons could reduce growth of juvenile pink salmon.