The envelope of human T-cell leukemia virus type I (HTLV-I) consists of two glycoproteins gp46 and p20E. Recombinant envelope proteins were produced by using an expression vector derived from insect baculovirus, Bombyx mori nuclear polyhedrosis virus. Polyhedrin fusion proteins C182, N147, and N287 contained whole region p20E, C-terminal half of gp46, and almost whole region gp46, respectively. N147 and N287 were suggested to be processed forms resulting from internal cleavage by cellular enzymes. In cultured cells and the insect larvae, C182 and N147 were produced abundantly enough to be purified to homogeneity; however, N287 was produced poorly and not purified. The purified proteins were recognized by HTLV-I-infected human sera and shown to be highly specific antigens for blood screening systems.