Juvenile starry flounder (Platichthys stellatus) maintained at 4 degrees or 12 degrees C were forced-fed 3H-1-naphthalene. At 24 hr, after the initiation of exposure, significantly (p less than 0.05) higher concentrations (2 to 15 times) of naphthalene were present in tissues of starry flounder at 4 degrees C than those present in fish held at 12 degrees C. The influence of lowering of water temperature on naphthalene retention was even more marked after one week. At this time, muscle and liver of fish at 4 degrees C contained 26 and 34 times, respectively, more naphthalene than did muscle and liver of fish at 12 degrees C. Concentrations of total metabolites, in most tissues were not substantially higher at the lower temperature either 24 or 168 hr after the naphthalene-exposure. Thin-layer chromatographic separation of the metabolites revealed that at 24 hr, 1,2-dihydro-1,2-dihydroxynaphthalene (dihydrodiol) was the major component in liver (40 to 50% of extracted metabolites) and muscle (approximately 80% of extracted metabolites) regardless of the temperature. Bile contained, primarily conjugates (e.g., glucuronides), which yielded the dihydrodiol as the principal metabolite on enzymatic hydrolysis. From 24 to 168 hr, the concentrations of each metabolite class did not vary directly with the concentrations of total metabolites. Accordingly, at 168 hr, the ratio of total metabolite concentrations in liver of fish at 4 degrees C compared to 12 degrees C was 1.6, whereas the ratios for the dihydrodiol, sulfate/glucoside conjugates and glucuronide conjugates were 4.5, 0.6 and 3.8 respectively. Generally, lowered water temperature increased tissue concentrations of the parent hydrocarbon and its metabolites. However, the magnitude of the increase was dependent upon the compound, the tissue, and the time after the initiation of the exposure. The results emphasize the importance of determining concentrations of individual metabolites together with parent hydrocarbons in tissues of fish when assessing effects of environmental parameters on xenobiotic toxicity.