Axillary odor is known since 50 years to be formed upon the action of Corynebacteria on odorless axilla secretions, but the nature of the bacterial enzymes involved in this process remained a mystery. We identified the known axilla odor determinant 3-methyl-2-hexenoic acid in hydrolyzed axilla secretions along with a new, chemically related compound, 3-hydroxy-3-methyl-hexanoic acid. The natural, odorless precursors of both these acids were purified from non-hydrolyzed fresh axilla secretions. The malodorous acids were shown to be covalently linked to a glutamine residue in fresh axilla secretions. Corynebacteria, but not Staphylococci, isolated from the axilla were found to release the acids from these precursors in vitro. A Zn(2+) -dependent aminoacylase mediating this cleavage was then purified from Corynebacterium striatum Ax20 and the corresponding gene agaA was cloned and heterologously expressed in Escherichia coli. Based on these biochemical findings, novel approaches in research on axilla malodor control are presented: (a) With a new test method using the isolated Corynebacteria and their enzymatic activity, the direct malodor-controlling activity of existing cosmetic ingredients was evaluated. (b) The structure of the natural malodor precursor was modified by replacing the malodor acid with fragrance molecules. These new fragrance precursors were shown to be cleaved by the same aminoacylase.