The activities of enzymes associated with xenobiotic metabolism and/or oxidative processes, and the levels of aromatic-DNA adducts, have been determined in the livers of grey mullet (Oedalechilus labeo and Lisa ramada) living in two eastern Mediterranean harbours. Glutathione peroxidase (GSH-P) activity was 2.5 times higher (similar to 9 IU g(-1) liver) and glutathione reductase (GSSG-R) activity was twice as high (similar to 2.5 id g(-1) liver) in fish from the more polluted harbour at Mersin than in the harbour near Erdemli. Superoxide dismutase (SOD) activity was 25% lower (4.3 IU g(-1) liver) in the more polluted harbour. The concentrations of glutathione and malondialdehyde varied both with species and environment by a factor of 2.5-3. DNA adducts in liver were determined by P-32-postlabelling. In Oedalechilus labeo in the more polluted harbour, adduct levels were 258 +/- 21 adducts per 10(8) nucleotides (mean +/- SE); two groups of Lisa ramada were distinguished having 261 +/- 48 and 30 +/- 6 adducts per 10(8) nucleotides, respectively. The average adduct level in a group of mullet of mixed species in the less polluted harbour was 3.3 +/- 2.3 adducts per 10(8) nucleotides. The results illuminate the ability of mullet to live in contaminated marine environments, and show that enzyme activities and liver DNA adduct levels can serve as indicators of marine pollution.