A review with 100 refs. The enormous potential of combinatorial approaches for studying problems in biol. and chem. has been clearly demonstrated over the last several years. In particular, phage display has become one of the major techniques for the use of combinatorial peptide and protein libraries. The reasons for the success of phage display are, at least, threefold: (1) phage display of combinatorial libraries creates a direct link between phenotype (the selectable properties of interest from the displayed library) and genotype (their sequences); (2) it offers the possibility to select and amplify single clones out of large libraries; (3) it allows in vitro as well as in vivo selections in order to evolve peptides and proteins with novel activities. Reported applications include selections of peptides as lead compds. in pharmaceutical research, redesign of protein structures and protein-protein interactions, screening of cDNA libraries and enzyme design. This diversity in applications has been made possible by the development of a variety of display formats and selection schemes and an increasing understanding of the biol. of filamentous bacteriophages. This review aims to provide the reader with a general overview of the tremendous possibilities of the technol. as well as its limitations. Selected examples will be used to highlight the current state of the art, although these examples represent only a fraction of all the interesting expts. and techniques that have been developed over the last few years. [on SciFinder (R)]