Recombinant proteins engineered to have six consecutive histidine residues on either the amino or carboxy terminus can be purified using a resin containing nickel ions (Ni(2+)) that have been immobilized by covalently attached nitrilotriacetic acid (NTA). This technique is know as metal-chelate affinity chromatography and can be performed using either native or denatured protein. This unit presents protocols for expression of histidine-tail fusion proteins and their purification in either native or denatured form (along with procedures for renaturation by either dialysis or solid-phase renaturation). Also provided are procedures for analysis of the purified produce and regeneration of the NTA resin.