Previously we had reported the production of an antiserum to an antigen found primarily in germ cells of the Indianmeal moth, Plodia interpunctella (Zimowska et al., 1991). The antigen, molecular weight 25,000 kDa, and a related protein, molecular weight 21,000 kDa, co-purified with the follicular epithelium yolk protein. Antisera to the two proteins were raised, and they both reacted with the same four small polypeptides, which had molecular weights of 20,000, 21,000, 25,000 and 28,000 kDa, that were present in the eggs throughout embryogenesis. A 30 amino acid sequence of an internal fragment of the 25,000 kDa molecular weight polypeptide showed sequence similarity with the alpha-crystallin A chain polypeptides from the lenses of vertebrate eyes and, to a lesser extent, with small heat shock proteins. Based on the sequence similarity with the alpha-crystallins, we suggest that this family of polypeptides from the germ cells of this moth be considered as cognates of the alpha-crystallins, and the 25,000 molecular weight polypeptide described here be given the designation ac25. Using immuno-gold labeling with antiserum to ac25, the alpha-crystallins were shown to be distributed throughout the cytoplasm and nucleoplasm of the oocyte and nurse cells, but not present within yolk spheres or other organelles of the oocyte or nurse cells. Immunofluorescent staining of males showed antigenic material in the sperm bundles within the testes. Oenocytes of the pupal and adult stages also contained cross-reactive material.