The concomitant administration of Indomethacin reduced the biochemical signs of the nephrotic syndrome induced in rats by aminonucleoside; in the rats treated with both drugs a morphological picture suggesting activated function of podocytes was found at the electron microscopic examination of the renal glomerular structures, together with the lesions characteristic of the aminonucleoside nephrosis. The possibility is discussed that Indomethacin could modify the permeability of the glomerular capillary wall by stimulating thepodocytes to synthesize basement membrane material.