CDNA concatamer sequencing; a method for increasing the efficiency of sequencing cDNA library subclones cDNA fragments are cleaved with a restriction nuclease and randomly religated into larger DNA fragments (mis-named concatamers), which are then randomly sheared and the ends, repaired. A 5'-overhanging adaptor is ligated to them, which allows their insertion into a vector which has been prepared by leavage and religation with complementary oligonucleotide 5'- overhangs. The vectors with inserts are used for transfection. When these inserts are sequenced, the artificial junction between religated fragments may be recognised by the presence of the restriction site. The method increases the efficiency of sequencing of what would otherwise be 3'-ends of fragments, which are less likely to be successfully sequenced.