We examined the ultrastucture of postmeiotic spermiogenesis in the testis of Helicoverpa assulta. Like other Lepidopterian species, tobacco bud worm produces two kinds of sperms-nucleated eupyrene and anucleated apyrene. We emphasized the structural differentiations of the eupyrene head. In elongating spermatids, acrosomes have a long projection and come close to the side of the nucleus. Chromatin scattered inside the nucleus is transformed into a granular structure and then becomes compactly condensed within the inner membrane. Cytoplasm progressively disappears and reticular appendages are attached on the outer membrane. In maturing sperm, acrosomes become very short in length and form narrow channels around the nucleus. An electron - dense nucleus, one centriole, extracellular material, and the ultrastructure of a 9+9+2 flagellum appears in each maturing sperm. Mature sperms are linked by cytoplasmic bridges to form a single clone and almost all of the cytoplasm disappears. In fully mature sperm, reticular and lacinate appendages show up whereas extracellular material disappears.