A review. Directed evolution consists of repetitive cycles of random mutagenesis of the protein/peptide sequence followed by screening or selection of candidates with desired properties. Many different approaches are used to introduce mutations into a gene; most of the currently used are error-prone polymerase chain reaction (PCR), DNA shuffling, and satn. mutagenesis. On the other hand, the techniques used in screening or selection expts. range from facile colony activity screening to yeast two-hybrid systems or in-vitro selection display systems such as phage display, mRNA display, and ribosome display. All these approaches have been used to alter protein function, to increase the activity or soly. of proteins, or to adapt enzymes for industrial applications. And, although none of these approaches provides the ultimate soln. to the directed evolution of proteins, numerous examples of successfully altered and improved proteins clearly show the power of directed evolution for protein design. [on SciFinder (R)]