The present invention relates to biocidal compositions comprising at least one biocidal active substance and at least one solvent from the group of polyglycol monobutyl ethers, and to their use as preservatives and disinfectants. More specifically, the invention provides compositions comprising a) at least one biocidal active substance b) at least one solvent according to the formula I R—(O—CH2—CH2)x—O—H  (I) in which R is a linear or branched butyl group and x is a number from 3 to 10.