The in vitro evaluation of the antibacterial, antifungal and DNA-damaging properties of some 1,2-benzisothiazolin-3-one derivatives is described. Antibacterial activity against Gram+ microorganisms (Bacillus subtilis and Staphylococcus aureus) was demonstrated in some N-alkoxybenzyl, N-aryl and N-alkoxyphenyl derivatives. Antifungal activity turned out to be strongly affected by the substituents considered. Some derivatives exhibited selective activity against the fungi used. Poor antimicrobial activity was observed in the N-chlorocarbonylphenyl and N-carboxyamidophenyl derivatives. None of the compounds tested turned out to have any genotoxic properties.