The invention relates to biocidal substances containing at least one isothiazolinone from the group consisting of 1,2-benzisothiazolin-3-one (BIT) and 2-methyl-4-isothiazolin-3-one (MIT) and at least one N-alkyl-guanidinium salt, to methods for the production thereof and to the use thereof for protecting against technical materials and products which can be infected by micro-organisms.
