To increase the efficiency of photoaffinity labeling of DNA polymerases, a binary system of photoaffinity reagents was applied. Photoreactive radioactive primers were synthesized by DNA polymerases beta (pol beta) or DNA polymerase from Thermus thermophilus (pol Tte) using a template-primer duplex in the presence of a dTTP analogue containing 4-azidotetrafluorobenzoyl group linked via spacers of varying length to 5-position of uridine ring-5-[N-(2,3,5,6-tetrafluoro-4-azidobenzoyl)-amino-trans-propenyl-1]-2 ' -deoxyuridine-5 ' -triphosphate (FAB-4-dUTP) or 5-[N-[[(2,3,5,6-tetrafluoro-4-azidobenzoyl)butanoyl]-amino]-trans-3-amin opropenyl-1]-2 ' -deoxyuridine-5 ' -triphosphate (FAB-9-dUTP). The reaction mixtures were UV irradiated (lambda = 365-450 nm) in the absence or presence of a dTTP analog, containing a pyrene moiety-5-[N-(4-(1-pyrenyl)-butylcarbonyl)-amino-trans-propenyl-1]-2 ' -deoxyuridine-5 ' -triphosphate (Pyr-8-dUTP) or 5-[N(4-(1-pyrenyl)-ethylcarbonyl)-amino-trans-propenyl-1]-2 ' -deoxyuridine-5 ' -triphosphate (Pyr-6-dUTP). The most efficient crosslinking of both DNA polymerases was observed in the case of photoreactive DNA primer, carrying the FAB-4-dUMP moiety at the 3 ' -end, and Pyr-6-dUTP as a sensitizer. The binary system of photoaffinity reagents allows increasing photoaffinity labeling of the both DNA polymerases in comparison to the primer crosslinking without photosensitizer.