The procedures for calmodulin-tagged phage and two-filter sandwich assays for the isolation of enzymic activities are presented. In the first method, enzymes are displayed on filamentous phage, and the reaction substrate is anchored on the calmodulin-tagged phage-enzymes using a calmodulin binding peptide. In the second method, enzyme mutants are expressed in bacterial colonies on a porous "master" filter, and the enzymes are released and diffuse to a second reaction filter that closely contacts the master filter. [on SciFinder (R)]