The present study was designed to investigate the association between levels of organochlorine pesticides (OCPs) and liver enzyme responses in Cyprinus carpio. Fish were caught at three stations in the Buyuk Menderes River (BMR): the origin, the Saraykoy station, and the estuary. Seventeen OCPs were quantified in liver tissue, as well as in river water by gas chromatography (GC)-electron capture detection, and structures were confirmed by negative chemical ionization-GC-mass spectrometry. The activities of CYP1A, GST, Se-GPx, CAT, and SODs were determined by spectrophotometry or fluorimetry. The mRNA levels of CYP1A, GST, and SOD1 were quantified by real-time RT-PCR. CYP1A and antioxidant enzyme activities were dramatically higher at the Saraykoy station, where OCP pollution is higher than the other two stations. Mn-SOD is responsible for the increase in total SOD activity in the Saraykoy samples. However, gene expression levels of certain enzymes were heavily suppressed. Our findings show that the transcriptional and functional responses of CYP1A and antioxidant enzymes are inversely correlated. (C) 2014 Published by Elsevier Ireland Ltd.