Certain amino-acid derivatives are disclosed as effective inhibitors of human leukocyte elastase and therefore useful in preventing the imbalance of this proteolytic enzyme in vivo. The compounds specifically are derivatives L-valine, L-norvaline, L-norleucine, and L-methionine methyl ester azolides succinimides or pyridones and sulfonate salts, and related compounds such as L-leucine and L-phenylalanine methyl ester derivatives. The compounds were found to be excellent inhibitors in that they embody both inhibitory and anti-oxidant or anti-inflammatory activity.