A new original vector pEM-(dT)40(f+) has been prepared. It can be used for cDNA library construction from polyadenylated mRNA, isolated from various sources. The pGEM-(dT)40f(+) is initially transformed into single stranded and then into a linear form and its (dT)40 tail at 3'-end is used as the vector-primer for synthesis of the first strand cDNA. The use of a synthetic oligonucleotide complementary to the vector and recombinant DNA results in vector cyclization and synthesis of the second strand cDNA. This approach significantly simplifies cDNA library construction, it does not require PCR reaction (which can induce artifact mutations in cDNA sequences) and restrictase treatment.