Tetraazaporphins represented by the general formula (I): ##STR1## provide substances derived from organisms (e.g. antigens, antibodies, nucleotides, etc.) which have been labeled with a fluorochrome for labeling comprising the tetraazaporphin; reagents comprising any of the labeled substances which can be utilized for assay of various antigens, drugs, DNAs and the like; and analysis of the base sequence of DNA. Fluorescence analysis can be carried out using the labeled substances.