The alkaline extracellular protease (AEP) gene ( XPR2) of the yeast Yarrowia lipolytica was cloned using synthetic oligonucleotide probes based on the N-terminal amino acid sequence of mature AEP. The XPR2 gene codes for a predicted precursor polypeptide of 46903 Da and a mature AEP of 30524 Da. We have increased XPR2 gene copy number by successive integration of XPR2-LYS5 and XPR2-URA3 vectors obtaining strains with one, two and three copies of the XPR2 gene at the XPR2 locus. A disrupting vector xpr2::LYS5 was used to construct a control strain with no XPR2 gene. We have also used a XPR2-LEU2-ars18 replicative vector to transform the disrupted strain. By measuring AEP produced by these strains, we observed a linear increase of AEP secretion with gene copy number.