Pectinophorin, the predominant soluble protein in the hemolymph of diapausing pink bollworm larvae, Pectinophora gossypiella (Saunders), was undetectable in the hemolymph of actively feeding larvae and became detectable in some larvae at the start of the post-feeding wandering stage before diapause conditions were imposed. Thereafter, pectinophorin increased in titre from 0 to an average of 142.2 ng/ l in the hemolymph in the middle of a 30 day diapause induction period (13 C; 10:14; L:D). Fifty days after the start of diapause (early diapause), the titre of pectinophorin increased to 222.4 ng/ l and 90 days after the start of diapause peaked at 507.8 ng/ l, which was about 40% of the total hemolymph protein.