Hepatic ethyoxycoumarin O-deethylase (ECOD) and ethoxyresorufin O-deethylase (EROD) activities, and serum sorbitol dehydrogenase (s-SDH) were measured over 3 years in sand flathead (Platycephalus bassensis) collected from Port Phillip Bay, Australia. Significant enzyme induction generally occurred in regions closest to highly industrial and urbanized areas relative to undeveloped reference areas of the bay. High s-SDH levels were associated with lower hepatic microsomal ECOD and EROD levels. There were no sex differences in liver ECOD or s-SDH in any sampling period, and sex differences in EROD activity were only significant in September 1990, when males had significantly higher activities than females (47.0 pmol min-1 mg protein-1 compared with 28.4 pmol min-1 mg protein-1, respectively). Liver EROD activity in sand flathead from Hobsons Bay was positively correlated with total freshwater input, mainly from the Yarra River, suggesting PAHs as a possible cause of the observed induction.