Novel uses of porphyrin compounds

The invention provides the use of a compound of Formula (I), or metallated derivative thereof, in the preparation of a medicament for killing or attenuating the growth of microorganisms by a method which does not comprise exposing the compound to a photodynamic therapy light source or a sonodynamic therapy ultrasound source Formula (I) wherein X1, X2, X3, X4, Yi, Y2, Y3, Y4 and Z have meanings given in the description. Preferably, the microorganisms are selected from the group consisting off bacteria, mycoplasmas, yeasts, fungi and viruses.