BACKGROUND Vasa (a DEAD-box helicase, also known as Ddx4) is an ATP-dependent RNA helicase highly conserved among all animals. Research on the presence and function of DDX4 in female mammals is limited. To gain greater insight into its distribution and role in female mice, we detected the expression of DDX4 protein in the ovaries and analyzed its expression pattern. MATERIAL AND METHODS MVH was detected in the cytoplasm of oocytes in all non-apoptotic follicles. RESULTS In the present study, we found that higher expression levels of ~55-60 kDa MVH isoform in the ovaries were followed by the accumulations of preovulatory follicles. CONCLUSIONS Higher levels of MVH protein in the ovaries might prepare oocytes for the competence to resume meiosis.