The invention relates to a preparation for the photodynamic control of micro-organisms, said preparation being in a liquid or pasty form and containing a photosensitiser which comprises a dyestuff and produces singlet oxygen when irradiated by means of light. The micro-organisms can be marked by means of the dyestuff. The aim of the invention is to improve said preparation in order to enable an improved photodynamic control. To this end, the preparation contains an active ingredient for amplifying or weakening the oxidative action of the singulet oxygen by chemical manipulation of the dyestuff or the nanoenvironment thereof. In a particular form of embodiment, a rinsing solution is used before the irradiation.
