HORMA-domain containing proteins are involved in cell cycle regulation by interactions with chromatin. Through an in silico subtractive screen for mouse genes preferentially expressed in newborn ovaries, we identified a gene that would encode a novel mammalian HORMA domain-containing protein termed Newborn Ovary HORMA protein (Nohma). Reverse transcription polymerase chain reaction and Northern blot analysis have demonstrated a 1.7 kb transcript that is expressed exclusively in germ cells in both male and female mouse gonads. Nohma expression can be detected postnatally in male, and prenatally in female gonads, but shows a sexually dimorphic expression in adult gonads. The Nohma transcript is abundant in the adult testis but limited in the adult ovary. The mouse Nohma gene is comprised of 15 exons and maps to chromosome 3. A human ortholog was also identified. The expression pattern of Nohma suggests that it may be a critical regulatory protein in germ cell meiosis.