Nine tetracycline (Tc)-resistant clinical isolates ofEnterococcus faeciumwere screened for plasmid content using agarose gel electrophoresis. pKQ10, a 1.9-kb plasmid carrying a novel Tc resistance determinant, was isolated from one of the isolates. The nucleotide sequence of this plasmid revealed an open reading frame corresponding to an 11.8-kDa protein and containing 105 amino acid residues. There was some limited similarity between this protein andtet(M),tet(O),tet(Q),tet(S),tetB(P), andotr(A), which overlapped, but did not include, the consensus GTP-binding sequences. The low-level, Tc-resistant determinant of pKQ10, namedtet(U), does not appear to correspond to any other known Tc resistance determinant.