The present invention relates to storage-stable biocidal compositions comprising at least one halogen-free isothiazolinone such as in particular 2-methyl-2H-isothiazol-3-one (MIT) and/or 1,2-benzisothiazolin-3-one (BIT) and/or salts thereof, and also stabilizing amounts of copper(II) ions, to a method for preserving technical materials by means of the aforementioned biocidal compositions, and to the technical materials treated therewith.
