The vitellin specific antisera were obtained from mice immunized with ammonium sulfate precipitate ovarian extract of the shrimp, Metapenaeus affinis and the vitellogenin specific antisera were produced by immunization of mice with precipitate from a mixture of anti-vitellin antiserum and haemolymph of the female shrimp. Specificity of both antisera was determined by double immunodiffusion against antigens from various shrimp species and by immunoelectrophoresis. The antigens from ovarian extract and from female hemolymph of M. Affinis and M. ensis show higher degree of similarity than the antigens from overian extract and from female hemolymph of the tiger prawn Penaeus monodon. Cross-react of both antisera to the antigens from ovarian extract and female hemolymph of the giant fresh-water prawn Macrobrachium rosenbergii, and from testicular extract and male hemolymph of M. affinis were not observed. The anti-vitellin antiserum also contain antibodies against other components in ovarian extract as well as the anti-vitellogenin antiserum contain antibodies against other components in blood. However, those antibodies in the anti-vitellogenin antiserum could be eliminated by absorption of the antiserum with hemolymph from the male M. affinis. Both antisera showed similar consistency for determination of vitellogenin levels in the hemolymph of M. affinis by competitive ELISA method. However, when the anti-vitellin antiserum was used, the high concentration of female hemolymph from M. affinis could not completely block the binding of antibodis to the ovarian antigens where as it could when the anti-vitellogenin antiserum was used. The anti-vitellogenin antiserum can be used to determine the levels of vitello-genin hemolymph of M. ensis as well. The relationship between vitellogenin levels in the hemolymph and ovarian development was surveyed from blood samples of M. affinis at different stages of ovarian development (I to IV) and post spawning. During the resting stage of the ovarian development (stage I), the hemolymph vitellogenin level was very low (about 0.193 (+,-) 0.167 mg/ml) compare to the growing stage (II & III) which was high about 2.343 (+,-) 0.906 and 2.673 (+,-) 0.951 mg/ml. The level of vitellogenin in the hemolymph decreased to about 0.708 (+,-) 0.508 mg/ml during the riping stage (stage IV) and rising up to various degress after spawning (spent

15.351 (+,-) 12.330 mg/ml). The vitellogenin levels of some hemolymph samples from M. affinis with ovarian development stage II or III were unusually high. It is possible that the high levels of vitellogenin in blood may be result from degeneration of the early growing ovary and from resorption of vitellogenin into the circulation. This evidence was confirmed by determination of hemolymph vitellogenin of shrimp with ovarian development stage II, III and IV after mainatined in captivity for 24 hours. After 24 hours in captivity the vitellogenin levels in hemolymph strikely increased in shrimp with ovarian development stage II and early of stage III but slighly changed in shrimp with ovarian develoment at late of stage III. The hemolymph vitellogenin levels in post spawning shrimp were quite variable depending on the amount of unspawned eggs remained in the ovary and gradually decreased to the low levels within 7 days.