Reversible tetracycline-dependent gene regulation allows induction of expression with the tetracycline repressor (TetR) or gene silencing with the newly developed reverse mutant revTetR. We report here the implementation of both approaches with full regulatory range in gram-positive bacteria as exemplified in Bacillus subtilis. A chromosomally located gene is controlled by one or two tet operators. The precise adjustment of regulatory windows is accomplished by adjusting tetR or revtetR expression via different promoters. The most efficient induction was 300-fold in the presence of 0.4 microM anhydrotetracycline obtained with a Pr-xylA-tetR fusion. Reversible 500-fold gene knockouts were obtained in B. subtilis after adjusting expression of revTetR by synthetically designed promoters. We anticipate that these tools will also be useful in many other gram-positive bacteria.