Compositions having broad effectiveness against bacteria and fungi, which comprise (a) an iodopropynylbutyl compound and (b) one or more formaldehyde donor compounds, the formaldehyde donor compounds being N-formals, O-formals and/or a combination thereof. The compositions are also stable and effective in the form of liquid concentrates. The present invention also relates to the use of such compositions in industrial products and to industrial products which comprise these compositions.