We have shown that the uvrD gene product, previously identified in maxicell extracts as a 73 kilodalton protein, copurifies with single stranded DNA-dependent ATPase and ATP-dependent DNA helicase activities. This protein is specifically precipitated from maxicell extracts by antibodies raised against DNA helicase II. In order to facilitate purification of the UvrD protein we have subcloned the uvrD gene into a plasmid vector in which its transcription is under the control of the phage lambda leftward promoter. Using cells harbouring this recombinant plasmid as a source of elevated levels of the UvrD protein we have purified this protein to homogeneity by a simple, rapid procedure. The purified protein has single stranded DNA-dependent ATPase activity and ATP-dependent DNA helicase activity, and both activities are specifically inactivated by antibodies raised against DNA helicase II. We conclude that DNA helicase II is the uvrD gene product.