To expand the scope of antibody-catalysed reactions to those involving rate-limiting proton abstraction, such as elimination, isomerization and condensation reactions, we developed a new strategy--hapten charge complementarity. A hapten containing a benzyl ammonium group was used to elicit a specific base, a carboxylate, in the combining site of an antibody that catalysed a beta-elimination reaction. This was the first example of the use of a hapten to elicit a specific catalytic residue in an antibody combining site. A variety of kinetic and chemical modification experiments strongly suggest that a specific Asp or Glu residue in the combining site is responsible for catalysis. Preliminary results indicate that in addition to charge-charge complementarity, the nucleophilic reactivity of amino acid residues (Ser, Thr, Lys, Asp, Glu, Cys) in antibodies can be used as a selection tool. Antibodies were raised against a reactive epoxide group to elicit an antibody containing a uniquely reactive carboxylate or thiol group. Antibodies which bind the epoxide do catalyse a beta-elimination reaction, indicating the presence of a specific base in the combining site. Antibodies elicited to two closely related haptens do not catalyse the beta-elimination reaction.