none The proteins synthesized by teratocytes of the braconid wasp Perilitus coccinellae were analyzed electrophoretically. Non-denaturing polyacrylamide gel electrophoresis (PAGE) revealed that the teratocytes contained a major polypeptide with a high molecular weight of about 540 kDa. SDS-PAGE indicated that the major subunit of this protein was approx. 94 kDa. The teratocytes were cultured in vitro in a medium containing 35S-methionine. Both the proteins from the incubated teratocytes and the medium were subjected to PAGE followed by fluorography. The fluorogram revealed that the teratocytes synthesized the 540 kDa protein. RNAs extracted from the teratocytes, parasitoid larvae and host fat body were translated in vitro in a rabbit reticulocyte lysate. Only the translation products of teratocyte RNA reacted with the antibodies generated against the crude teratocyte extract. Changes in the total protein content of teratocytes and parasitoid larvae indicated that the teratocytes may have a role in providing nutrients for the developing parasitoid larvae during parasitism. This hypothesis was supported by the fact that the gut contents of the parasitoid larvae showed an immunoreaction to antibodies against crude teratocyte proteins.