Repertoires of antibody (Ab) V genes derived from nonimmunized human donors (1 ) or made synthetically (2 3 ) have been cloned for display on filamentous bacteriophage as either scFvs or Fabs fused to the minor phage coat protein (pIII) (4 ). Phage Ab repertoires can be subjected to multiple rounds of panning on individual immobilized antigens (Ags) in order to isolate individual Ag-binding clones. This approach has been successfully applied to numerous purified soluble molecules, yielding high-affinity Abs (5 ). Selection against almost any soluble Ag is now theoretically feasible.