Drastic biochemical changes were produced in liver and muscle of common carp; Cyprinus carpio L. exposed to sublethal levels (V4 and Yz LC50) of either copper, cadmium or zinc alone or a combination of them for 7 and 30 days. The pattern of changes in both treatments was nearly the same except for the intensity of change. The hepatic aspartale amninotransferase (AST) in liver was increased, while acid phosphatase (ACP) activity generally decreased in fish exposed to high level of Cu, Cd, Zn and their mixtures. Also, hepatic alanine aminotransferase (ALT) showed significant increase in fish exposed to all mixture groups, except high level of Cu+Cd+Zn on the 701 day, and then the activity decreased on the 30th day in fish of all treated groups. In muscle, AST showed significant increase in fish exposed to low level of Cu, Zn, Cu+Cd+Zn and high level of Cu and Cd for 7 days. These values decreased significantly after exposure to low level of Zn, Cu+Cd, Cu+Cd+Zn as well as high level of Zn and Cu+Cd+Zn for 30 days. The activity of ALT was increased significantly on the 7th day in fish exposed to low level of mixtures of Cu+Zn, Cd+Zn and Cu+Cd+Zn as well as high levels of Cu, Cd, Cu+Zn and Cu+Cd+Zn treatments, while fish exposed to low level of Cu+Cd+Zn and high level of Cu+Zn, Cd+Zn and Cu+Cd+Zn treatments showed significant decrease in ALT activity on the 30th day. There was no significant change in muscle ACP activity in all treated fish groups.