The present study was undertaken to whether EDTA exerts beneficial effect on the development of mouse embryos derived from eggs fertilized in vitro. Superovulated eggs were collected from ddY females and were inseminated with epididymal sperm obtained from ddY males. At 6 hours after insemination the fertilized eggs were transferred to the Whitten's medium with or without EDTA and then cultured for 24 to 120 hours. The development of embryos beyond the 2-cell stage at 48 hours was significantly enhanced by the presence of 10 mM EDTA. Fifty seven per cent of embryos cultured for 96 hours in the medium containing EDTA developed morulae stage. Only 13% of embryos cultured for 96 hours in the medium without EDTA developed into morulae stage. On the other hand, 27% of embryos cultured in the medium with EDTA developed into blastocyst stage. As a conclusion, the development of in vitro fertilized mouse embryos beyond the 2 cell stages in Whitten's medium was enhanced by the presence of EDTA.