Recombinant DNA methods are powerful, revolutionary techniques for at least two reasons. First, they allow the isolation of single genes in large amounts from a pool of thousands or millions of genes. Second, the isolated genes or their regulatory regions can be modified at will and re-introduced into cells for expression at the RNA or protein levels. These attributes help to solve complex biological problems and to produce new and better products in the areas of health, agriculture and industry. Both volume 154 and 155 include the descriptions of several useful new restriction enzymes and rapid methods for DNA sequence analysis, along with a number of other useful methods.