DNA polymerase I produced by infection of Escherichia coli K12 with the specialized transducing phage lambdapolA has been purified by a simplified procedure and shown to be identical with the enzyme produced by uninfected E. coli in all aspects which have been examined. The abundance of the enzyme in infected cells and the ease with which it may be purified will simplify the study of the enzyme's physical and chemical characteristics. In addition, the enzyme is now much more readily available for use as an analytical tool in nucleic acid sequence and structure studies.