Proteins that bind and protect nucleic acids from acid precipitation have been characterized from human and mouse plasma. In the present study, one protein from Mendole (Spicara maena) eggs was purified to homogeneity, by means of acetone fractionation and Sephadex G-100 gel filtration. The protein inhibited DNA replication, exerted by various DNA polymerases. Amino-acid sequence analysis in the amino terminus revealed a unique sequence. Its possible physiological role is discussed.