In order to express recombinant porcine TGF-${eta}1$ protein in a baculovirus expression system the entire TGF-${eta}1$gene containing extra amino acids at the N terminus was cloned into pFBa and pFBb of the Bac-To-$Bac^{TM}$ baculovirus expression system. One of the clones contained 106 extra amino acids and was designated pFBa-106 TGF-${eta}1$, and the other had 28 extra amino acids and was designated pFBb-28 TGF-${eta}1$. The orientation of the gene was identified with restriction enzyme mapping and PCR with internal TGF-${eta}1$ primers. Sf-9 cells were infected at a m.o.i. of 10 by the recombinant viruses generated from the two expected sizes of 55 kD and 46.4kD. these precursor forms of TGF-${eta}1$ with a polyclonal antibody against human TGF-${eta}1$. No mature form of TGF-${eta}1$ protein was detected on SDS gels and an immunoblot indicated that TGF-${eta}1$ precursor is not properlu processed in insect cells.