It is shown that dNTP(3'F) are terminators of DNA synthesis and may serve as very effective tools for DNA sequencing with E.coli DNA polymerase I and AMV reverse transcriptase. The dNTP(3'F) are found to be chain terminator substrates for calf thymus terminal deoxyribonucleotidyl transferase but not for calf thymus DNA polymerase alpha. The optimal dNTP(3'F) concentration for DNA sequencing by DNA polymerase I is found to be an order of magnitude lower than that of ddNTPs. dNTP(3'F) produce a more clear sequence pattern than do ddNTPs.