One of the greatest improvements in the use of clone libraries in genomic research was the introduction of library arrays by storing single clones in separate wells of microtiter plates. This not only makes clones practically immortal by keeping the plates at −80°C, but it also gives each of the clones a unique reproducible identity, which allows scientists in different laboratories to be certain to use the same biological material for their various experiments, thereby enabling them to compare their results in a much more meaningful way. Equally important was the development of high-density filters, whereby thousands of these clones are transferred directly from microtiter plate wells onto nylon membranes in a regular pattern. This opened, on the one hand, a convenient way to make such libraries available to a large number of scientists, because filter membranes can be easily distributed, and, on the other hand, allowed screening of several thousand clones of a library in parallel, with a single hybridization experiment.