Bacteriophage T4 gene 41 encodes a replicative DNA helicase that is a subunit of the primosome which is essential for lagging-strand DNA synthesis. A mutation, rrh, was generated and selected in the helicase gene on the basis of limited DNA replication that ceases early. The survival of ultraviolet-irradiated phage and the frequency of genetic recombination are reduced by rrh. In addition, rrh diminishes the production of concatemeric DNA. These results strongly suggest that the gene 41 replicative helicase participates in DNA recombination.