In the yeast Saccharomyces cerevisiae, mutations in the genes RAD51 or RAD52 result in severe defects in genetic recombination and the repair of double-strand DNA breaks, These genes, and others of the RAD52 epistasis group (RAD50, RAD54, RAD55 RAD57, RAD59 MRE11 and XRS2), were first identified by their sensitivity to X-rays(1). They were subsequently shown to be required for spontaneous and induced mitotic recombination, meiotic recombination, and mating-type switching (reviewed in ref, 2), Human homologues of RAD50, RAD51, RAD52 RAD54 and MRE11 have been identified(3-6). Targeted disruption of the murine RAD51 gene results in an embryonic lethal phenotype, indicating that Rad51 protein is required during cell proliferation(7,8). Biochemical studies have shown that human RAD51 encodes a protein of relative molecular mass 36,966 (hRad51) that promotes ATP-dependent homologous pairing and DNA strand exchange(9-11), As a structural and functional homologue of the RecA protein from Escherichia coli(3,9,12), hRad51 is thought to play a central role in recombination, Yeast Rad51 has been shown to interact with Rad52 protein(13-15), as does the human homologue(16), Here we show that hRad52 stimulates homologous pairing by hRad51. The DNA-binding properties of hRad52 indicate that Rad52 is involved in an early stage of Rad51-mediated recombination.