During embryonic development, insect vitellins (Vt) are degraded by limited proteolysis to yield a number of lower-molecular weight polypeptides. The aim of the present study was to identify these polypeptides in the embryo and to verify how they relate to Vt polypeptides deposited in the oocyte during vitellogenesis. To this end a panel of poly- and monoclonal antibodies (Pab, Mab) was raised against Vt polypeptides and employed by immunoelectrophoresis and immunoblotting on embryos belonging to different developmental stages. Through this approach three major staining patterns were observed. First, Mab 4 reacts with both polypeptides B1 and E20, suggesting that polypeptide B1 is gradually trimmed to yield polypeptide E20 in late embryos. Second, Mab 12 is specific for polypeptide A3 which is retained unchanged throughout embryogenesis. Third, Pab anti-A2 and Mab 13 show that polypeptide A2 is processed to yield polypeptide E9 through limited proteolysis. In conclusion, the staining patterns reported in this study show that Vt polypeptides in developing embryos of the stick insect Carausius morosus undergo at least two major processing events concerning polypeptides B1 and A2.