Since the advent of polymerase chain reaction (PCR), it has proven possible to clone complete genes, or parts of these, without having to construct the usually obligatory cDNA library. PCR cloning, however, is not without its own problems and limitations, such as the fidelity of the cloned sequence (1 ) and the fact that prior knowledge of the target gene sequence is required. It is for these reasons that the traditional cDNA library still has a valuable role to play in the isolation of any new gene.