DJ-1 was first identified as an activated ras-dependent oncogene product and was later also found to be an infertility-related protein affected by sperm toxicants such as ornidazole (OR) and epichlorohydrin. These findings suggest that DJ-1 has functions in both somatic cells and sperm. In this study, to determine the relationship between DJ-1 and an endocrine disrupter and to determine the functions of DJ-1 in sperm, in vitro fertilization experiments were carried out using eggs and sperm extracted from mice that had or had not been treated with OR. We found that the amount of DJ-1 in sperm and the efficiency of fertilization decreased with the increasing dose of OR to which the mice were exposed. The addition of an anti-mouse DJ-1 serum to sperm solution before the in vitro fertilization reaction with eggs resulted in a decrease in the efficiency of fertilization to about one-third of that when pre-immune serum was added to sperm solution, indicating that DJ-1 participates in the fertilization.