Cholinesterase (ChE) and ethoxyresorufin-O-deethylase (EROD) were of special interest to this study as these biochemical tools have been widely used for the determination of exposure to pollutants. In this study, the freshwater oligochaete Limnodrilus profundicola was tested for its potential as a bioindicator of freshwater pollution. For this purpose, the ChE and EROD activities of L. profundicola and the level of polycyclic aromatic hydrocarbons (PAH) of water samples collected from different sites along the Curuksu stream on the Menderes River (the ancient Meander) running through south-western Turkey were studied. First, these activities were characterized using, as model substrates, acetylthiocholine (ATC), propionylthiocholine (PTC), and butyrylthiocholine (BTC). Then, the in vivo effects of insecticides and pollutants on these activities were investigated. L. profundicola were exposed to various doses of methyl-parathion, methomyl, and deltamethrin. Although significant inhibition of ChE was detected with each of the insecticides, the highest level of inhibition was observed with methyl-parathion. In addition to the inhibition of ChE, the activity of EROD was induced by exposure to oil-contaminated sediments. Thus, although L. profundicola has a reputation for being very resistant to pollution (although it is not insensitive to it), we demonstrated that it may potentially be used as a bioindicator species for contaminant exposure when ChE and EROD are used as biomarkers. (C) 2010 Wiley Periodicals, Inc. Environ Toxicol 26:37-44, 2011.