The work described herein consists of the development of a general procedure for cloning and identifying double-stranded DNA fragments transcribed from specific mRNA sequences, contained within a mixed population of mRNA species. The procedure combines techniques of RNA purification, complementary DNA complexity analysis and recent advances in recombinant DNA technology. Using this approach it has been possible to obtain several clones which have been shown to contain DNA sequences derived from the mRNA that specifies chicken serum preproalbumin.