The coding region of the gene for Taq DNA polymerase has been cloned into the common vector pUC18. Using a single-step procedure, large amounts of active enzyme can be purified from Escherichia coli carrying this construct. This procedure takes advantage of the thermostable properties of the DNA polymerase. This simple procedure gives very high yields of essentially homogeneous, highly active enzyme suitable for use in molecular biological applications. Yields are over two orders of magnitude greater than available with current methods.