The insoluble complex formation between alpha-amylase and the strong anionic polyelectrolyte polyacrylic acid was studied by using turbidimetric and enzymatic activity. The highest molecular weight polyacrylic acid (100,000 Da and 240,000 Da) proved to be suitable precipitating agents. They were insoluble at pH lower than 4-5, with a stoichiometric ratio polymer mol per protein mol of 1:52 and 1:154, respectively. Electrostatic interactions are not the only factor in the formation of insoluble complexes. High percentage of alpha-amylase enzymatic activity maintains throughout time, even in the presence of polyelectrolyte. The application of precipitation conditions found when applying a bovine homogenate showed that it is not suitable for purification even if it proved to be useful methodology for the concentration of the enzyme and can be used as a first step of purification. (C) 2010 Elsevier Ltd. All rights reserved.