Female-specific protein (FSP, vitellogenin) in Penaeus monodon hemolymph and its related ovarian protein (vitellin, lipovitellin) were identified and characterized using electrophoretical and immunological procedures. The purification of vitellin from mature ovaries was carried out using hydroxylapatite and Sepharose 6B columns. Results indicated that there are two proteins specifically existing in the hemolymph of the mature female which are immunologically identical to ovarian protein. These are absent in the male. The isolated vitellin has a molecular weight of approximately 540 kDa and is composed of 4 major (polypeptide) subunits, 74, 83, 104 and 168 kDa and 1 minor (polypeptide) subunit, 90 kDa. The purified protein stained positively with periodic acid-Schiff and Sudan black B and thus is a glycolipoprotein. Results of double immunodiffusion demonstrate the cross-reactivity of P. monodon vitellin antiserum with the ovarian extract from mature females of Penaeus indicus, Penaeus merguiensis and Penaeus semisulcatus, but not with Pandalus kessleri, indicating that there is no antigenic difference at species level in Penaeidae.