Tetracycline resistance protein (TET) of Bacillus subtilis plasmid pNS1 was detected by immunoblot analysis using a specific antibody to TET-chloramphenicol acetyltransferase (CAT) fusion protein. In two-dimensional electrophoresis, one major spot which seemed to be the pNS1-encoded TET (pNS1-TET), was detected by immunostaining. Its molecular weight and isoelectric point were approximately 52 kDa and 6.2, respectively. Judging from the nucleotide sequence, the pNS1-TET is a very hydrophobic, 50 kDa protein. Therefore, the 52 kDa protein is thought to be an intact form of the pNS1-TET produced by B. subtilis cells.