Study of the renal vascular lesions of maturity diabetes with new staining methods shows that the fibrinous deposits in the vessel walls change to an acellular amorphous material staining as collagen. This pseudo-collagen is so clearly the end-result of an escape of plasmatic substances that a similar deposition may well follow the other forms of plasmatic vasculosis, hypertensive, static or hyperergic, this last being the probable basis of the so-called collagen diseases.