Bacteria are particularly convenient for producing recombinant proteins for purification purposes. Suitable extraction methods for bacterial cells include sonication, glass bead milling, grinding with alumina or sand, high-pressure shearing using the French pressure cell (French Press), and lysozyme treatment. These procedures are applicable for preparing extracts from a variety of gram-negative bacteria such as Escherichia coli and Klebsiella pneumoniae, and gram-positive bacteria such as Bacillus subtilis. Disruption of bacterial cells by enzymatic means is commonly used because a relatively uniform treatment is obtained when cells are in suspension. This protocol describes the enzymatic disruption of E. coli.