Alpha-1-antitrypsin (AAT) globules were incidentally demonstrated in the kidney tubules from the autopsy material in patients with PiMZ, PiZZ and PiMM phenotypes in our laboratory. This study was designed to study the pathological significance of this phenomenon. A total of nine cases were selected from the autopsy file, two patients with AAT PiZZ, four with PiMZ and three with PiMM were studied. Sections of liver and kidney were stained for AAT by indirect immunoperoxidase method. All of the PiMM patients showed positive reactions in most of the proximal and some of the distal tubular epithelium. Of the six cases with abnormal Pi, one failed to show any reaction, four showed weak positive staining in some of the proximal tubules and one with high serum AAT revealed relatively strong activity in most of the proximal tubules. These findings suggest that AAT is present in the renal tubular epithelium. Whether AAT globules are produced in the renal tubular cells or secondarily absorbed from the glomerular filtrate is unclear. The significance of stainable renal tubular AAT in normal subjects, in patients with abnormal protease inhibitor types and in patients with renal disorders, needs further clarification and study.