Pre-elafin, also known as trappin-2, is an elastase-specific inhibitor that belongs to the trappin gene family. A chimeric gene encoding polyhistidine-tagged human pre-elafin fused to the yeast a-factor precursor was expressed in Saccharomyces cerevisiae. The chimera was engineered to keep a single copy of the mature a-factor peptide. This enabled the use of a simple bioassay (mating assay) to assess the relative efficiency of both the expression and the secretion of the recombinant molecule, We found that pre-elafin is processed both in vivo and in vitro by yapsin 1, the yeast aspartyl endoprotease encoded by YPS1. Cleavage by yapsin 1 occurred C-terminal to a subset of single lysine residues. Expression in a yapsin l-deficient yeast strain was an indispensable condition to allow the efficient production of full-length human pre-elafin. The recombinant inhibitor was purified from concentrated culture medium by ammonium sulfate precipitation, affinity purification on a Ni2+ resin, and cation exchange chromatography, Recombinant human pre-elafin was fully active and showed the same inhibitory profile toward different serine proteases to that reported for mature elafin.