RESULTS I. Clinico-Pathologic Summary. Approximately 70 per cent of the F1 generation NZB/NZW mice (49 animals to date) spontaneously de-veloped nephropathy. In a majority of the affected animals this was ac-companied by anemia, proteinuria (with and without ascites), urinary casts, classic LE cells, hematoxylin bodies and antinuclear antibodies. Light microscopic examination of the kidney sections using conventional stains showed extensive glomerularalterations (Fig. i). Glomeruli were generally more cellular with basementmembrane thickening, occasional hematoxylin bodies and exhibited diffuse and verrucal fibrinoid degeneration. Treatment of kidney sections with fluoresceinated rabbit antimouse gamma globulin resulted in specific bright apple-green fluores-cence localized in thethickened glomerular basement membranes (Fig. 2). Blocking with non-fluoresceinated anti-sera abolished such fluores-cence.