Sensitivity of meiotic cells to DNA damaging agents is little understood. We have demonstrated that the meiotic pachytene nuclei in the Caenorhabditis elegans gonad are hyper-resistant to X-ray irradiation, but not to UV irradiation, whereas the early embryonic cells after fertilization and the full grown oocytes are not. The Ce-rdh-1 gene [RAD51, DMC1 (LIM15), homolog 1 or Ce-rad-51], which is essential for the meiotic recombination, is the only bacterial recA-like gene in the nematode genome, and is strongly expressed in the meiotic cells. Following silencing of the Ce-rdh-1 gene by RNA interference, the meiotic cells become more sensitive to X-ray irradiation than the early embryonic cells. This is the first report that meiotic cells are hyper-resistant to DNA strand breaks due to the high level of expression of the enzyme(s) involved in meiotic homologous recombination.