Dinocampus (= Perilitus) coccinellae (Braconidae: Hymenoptera) teratocytes synthesize a teratocyte-specific polypeptide (TSP) with a high molecular weight of 540 kDa. The TSP has a tendency to accumulate in the teratocyte cells without release after synthesis (Okuda and Kadono-Okuda, 1995), which was confirmed in this study. Pulse-chase fluorography indicated that teratocytes at a younger stage (6 days after parasitization) secreted negligible TSP into the medium after synthesis, while teratocytes at an older stage (11 days after parasitization) secreted the synthesized products into the medium, although the amount released was still low. Western blot with anti-TSP serum showed that only a small amount of TSP appeared in the parasitized host hemolymph, even when TSP synthesis by teratocytes was actively taking place, which also supported the accumulative nature of TSP. The immunoelectronmicroscopic studies revealed that the TSP was localized specifically in high electron-dense vacuoles. Lectin blot analysis identified TSP as a high mannose glycoprotein. The amino acid composition of the major subunit of the TSP was quite similar to that of nutritive proteins such as vitellogenin and storage proteins of some insects. These characterization data, together with the accumulation property of the TSP indicates that Dinocampus teratocyte primarily plays a nutritive role for the developing parasitoid larvae. TSP exhibited esterase activity, which indicates that TSP may have an additional function in the host-parasitoid reaction.