The tetracycline-repressible (TetOFF) system has found widespread applications in protein pharmaceutical production and gene therapy research, as an efficient and nontoxic means of controlling transgene expression in mammalian cells. One limitation, however, has been the lack of satisfactory ways of independently controlling expression of a second transgene. In this issue, Fussenegger and colleagues have developed such a versatile and complementary system regulated by the streptogramin family of human oral antibiotics. They combined a bacterial promoter element (PPTR) and a pristinamycin repressor, the Pip protein, with various promoters and viral transactivation domains, to create both streptogramin-repressible and -inducible systems that can work in combination with TetOFF in a variety of human cell lines (see p. 1203).