Abstract: The main aim of the present study was to investigate the effects of copper sulphate on the acetylcholine content, acetylcholinesterase and Na+K+ ATPase activity in various tissues of the fish Cyprinus carpio. These parameters were analysed in fishes exposed to the lethal concentration of copper sulphate for a period of 15, 30 and 45 min and subsequently for every one hour up to a period of 24, 48 and 72 h. Results indicate that the ACh levels, AChE and Na+K+ATPase activity showed variable pattern of increase and decrease, depending on the duration of exposure and the type of tissue involved. These tools are essential for improving the risk assessment process by understanding the sites and mechanisms of neurotoxicity and the effects of neurotoxicants.