Abstract: A method of producing cDNA from mRNA is described in which the 5' end of mRNA is capped and introduced into a vector so that both the 5' and 3' ends become annealed to flanking sequences of the vector. Reverse transcriptase is then used to convert the mRNA into dscDNA, the reverse transcriptase being employed in vivo, in vitro or using a combination of these approaches. Preferably, the conversion of mRNA to dscDNA is carried out in a cell line transformed with a second vector producing the reverse transcriptase, the cell line supplying the other enzymes and materials needed for cDNA synthesis. Also described are applications of this method to construct and screen cDNA libraries and cell lines transformed with both vectors.