Abstract: After HPDin sodium saline solution standing away from the light, NPSis formed. It shows an absorption/excitation peak at 403 nm, an emission peak at 580 nm. Its formation is strongly influenced by many factors, in particular, irradiation, temperature, pH, concentration and gases diluted in thesolution. NPSwas tentatively identified as a complexing intermediate ------"thesitting-at top complex" formed by combining HPDwith sodium ion in the solvent. The formation of NPSprobably brings about unfavourable influence upon the photosensitive capacity of HPDin cancer tissues.

Key words: Hematoporphyrin derivatives (HPD), New porphyrin species (NFS), The Sitting-at top complex