Microscopioal studies of the kidneys from six dogs (Canis familiaris) naturally infected by Leishmania donovani showed three cases of glomerular mesangial thickening and, in three other cases, a proliferative, focal, difuse and progressive glomerulonephritis. The auctor suggests that such alterations may be related to the Kala-azar infection and could probably be mediated through an immunological mechanism.