Meiotic cells of Coprinus contain a protein that can be identified by its ability to enhance activity of the meiotic DNA polymerase reported previously (8). Its activity is found only during the prophase stages in meiotic cells, and is accompanied by the meiotic polymerase. The protein, which was purified to near homogeneity, is a single polypeptide with a molecular mass of 30k, and shows no activities of nuclease, ATPase, or DNA-binding protein. The protein could enhance the meiotic polymerase activity by at least 5 fold. The other Coprinus polymerases were not influenced by the protein. The protein could increase Vmax value of the meiotic polymerase, but not the Km. The significance of this protein to meiotic DNA synthesis is considered in relation to other biochemical properties of meiotic cells.