A proteinaceous component eluted at the concentration of 0.8-1.0 M NaCl was obtained from hen egg white by heparin affinity chromatography. On SDS-PAGE, the component was resolved into three bands of 18. 5, 16. 5, and 16.0 kDa. The isoelectric point was estimated to be pH 8.8. This stimulated the DNA synthesis and proliferation of the cultured cells from chichen embryos. The amino acid composition and N-terminal analyses of the main 18.5 kDa component showed that this is a novel minor protein in egg white, and therefore was named “Ovofactor-1”.