α<sub>1</sub>-Antichymotrypsin (α<sub>1</sub>-AK) and α<sub>r</sub>antitrypsin (α<sub>1</sub>-AT) represent a defense mechanism to protect the tissues from proteolytic enzyme activity. We studied the implication of α<sub>1</sub>-AK and α<sub>1</sub>-AT in glomeruli of patients with different nephropathies based on the analysis of 52 paraffin-embedded renal biopsies with α<sub>1</sub>-AK and α<sub>1</sub>-AT antisera. The results demonstrate an intense α<sub>1</sub>-AK glomerular staining in renal biopsies from patients with minimal-change disease, while a minor staining of this protein was found in the other nephropathies. No significant evidence of α<sub>1</sub>-AT deposits was observed in our cases. Our findings suggest that when α-AK is lacking in glomeruli the defense mechanisms against proteolytic enzymes may not be efficient enough to protect the glomerular structures and limit the damage. Since α<sub>1</sub>-AK is a reactant of the acute phase of inflammation, it may be considered as a marker of activity for monocyte-macrophages in glomerular damage.