This invention provides methods for inactivating pathogenic contaminants in whole blood, plasma, cellular blood components, or in any combination thereof, by adding a phenthiazin-5-ium dye(s) thereto and irradiating said dye-containing composition for an effective length of time with light of wavelengths from 560 to 800 nm or red light, of an effective intensity, whereby the irradiation in conjunction with the dye(s) inactivate substantially all pathogenic contaminants contained therein. The methods of this invention inactivate pathogenic contaminants, such as viruses, bacteria and parasites, without substantially altering the whole blood, plasma, cellular blood components, or combinations thereof, such that they are suitable for transfusion.