of terminal-phosphate-labeled nucleoside-5???-pentaphosphates: [0171] wherein X is NH, O, S, or CH2, [0172] Y is NH, O, S, ONH, CH2, CO or another functional group capable of forming a covalent bond with the dye moiety and P is H or a leaving group such as halide or sulfonate. [0173] The invention is further described by reference to the examples below.