Binding-site repertoires with naturally rearranged v-genes are potentially heavily biased towards certain sequences and cloned, owing to evolutionary pressure and the immune history of the host. This will result in biases and redundancy in natural binding-site libraries. The use of laboratory-assembled variable-region genes would provide complete control over the genetic makeup, allow engineering of the individual building blocks, and a choice of where and how the diversity could be introduced in these repertoires. It was thought that with this possibilities, antibody libraries could be built with a high level of relevant diversity that might outperform the naive binding-site.