Existence of a non-phosphorylated female-specific protein (FS II), in addition to phosphorylated vitellogenin (FS I), in the plasma of murrel by exogenous administration of estradiol-17beta is reported. Polyspecific rabbit antibodies were raised against estrogen-inducible murrel plasma proteins. This antiserum was absorbed with normal male serum in order to obtain female-specific antiserum (FSAS). Radial immunodiffusion studies suggested that both the proteins (FS I and FS II) were present in the plasma of E2-treated and normal vitellogenic females and in the ovarian homogenate from gravid females, but absent in normal male plasma. Autoradiographic experiments demonstrated that phosphorus moiety was attached with FS I only. Further, immunoelectrophoretic analysis and peptide maps supported the observation that FS I and FS II were discrete, unrelated female-specific proteins.