A subtraction procedure was designed to isolated genes which are expressed only in normal mouse embryos while silent in mouse parthenogenons. Parthegenons are supposed not to express maternally imprinted genes, or if any at a very low level because their genome consists of only maternal haploid genomes. Total RNA was isolated from the parthenogenic embryos and normal embryos respectively. The RNA was then served as template fox cDNA synthesis. This cDNA was amplified by PCR. Partheongenic cDNA was used as driver DNA which eliminate cDNA common in both embryos from normal embryonic cDNA pool. Subracted DNA was then rescrened by differential hybridization method. Seven clones were selected and two of them were sequenced. These two sequences were absent in public databases. Instead, the sequence of one clone named Nep1 showed partial homologies with an EST sequence which was sequenced from cDNA library of human leg tissues. Northern blot analysis indicated that Nep1 is expressed specifically in testis. We are now trying differential methy1-sensitive Southern blot analysis with. the probe of Nep1 and its full length cDNA is under screening procedures with mouse testis cDNA library.