Adducts of certain unsaturated halides with hexamethylenetetramine are known to be effective germicides when present in concentrations as low as 0.01 percent in water-containing organic mixtures. However, under certain conditions the compounds may undergo detrimental spontaneous exothermic decomposition. Blending with the adduct an additament which undergoes an endothermic change at a temperature below that at which exothermic decomposition of the adduct decomposition thereby providing a composition stabilized for packaging and/or storage.