Two vitellins (Vn-1 and Vn-2) were identified in cockroach ovary. Vn-2 was purified by ion-exchange chromatography using DEAE cellulose and Sepharose CL-6B, and gel filtration using Sephadex G-200 and Sepharose 4B. Vn-2 comprises three subunits with molecular weights of 102, 72 and 40 kDa. Vn-2 contains diacylglycerol and triacylglycerol; their fatty acids are mostly lauric acid and palmitoleic acid. Vn-2 also has phosphatidylcholine and phosphatidylethanolamine but no sphingomyelin. Vn-2 contains large amounts of glutamic acid and aspartic acid but small amounts of tyrosine, phenylalanine, and methionine. Vn-2 gradually decreases during embryonic development; none remains in first instar larvae. It was found that Vn-2 partially reacted immunologically with ovarian extracts of Periplaneta fulginosa but not with those of Blattella germanica. Vn-2 also showed no immunological reaction with extracts from other orders; including Cletus schmidti (Hemiptera), Lucilia illustris (Diptera), Anechura japonica (Dermaptera), Bombyx mori (Lepidoptera), and Ducetia japonica (Orthoptera).