Apolipophorin-III (apoLp-III) was isolated from the last instar larval hemolymph of Spodoptera litura by cation exchange chromatography and reverse phase chromatography. Molecular mass of apoLp-III was estimated to be 18,266 daltons. Presence and exact localization of apoLp-III in both ovary and testis were identified by immunological analysis. In the earliest stage of ovary, apoLp-III is confined to the electron dense granules in the sheath cells between oogonia. During vitellogenesis, apoLp-III in the hemolymph is actively taken up into ovary through intercellular spaces between follicle cells and then stored in protein bodies in the ooplasm. After apoLp-III is taken up from the hemolymph into the basal portion of the vas deference, it is localized to electron dense granules on the apical surface of the vas deference epithelium. In in vitro culture study, after apoLp-III is actively synthesized in adult fat body, most of the synthesized apoLp -III is secreted to the medium.