The light and electron microscopical findings in the polyvinylpyrrolidine-storage disease are reported on the basis of biopsies of skin, striated muscle, bone marrow and liver from one patient and a subcutaneous nodule from another patient. Both patients suffer from diabetes insipidus and have been treated for several years with Insipidin retard, which contains polyvinylpyrrolidone (PVP) as the retarding agent. Deposits of PVP have been demonstrated in all the tissues examined and can easily be recognized by certain staining qualities. The combination of haematoxylin-eosin, elastin (Weigert), alkaline Congo red and Sirius red for amyloid and PTAH is specially to be recommended. The ultrastructural findings consist of intracellular vacuoles containing a granular material and probably representing lysosomes. The final identification of the nature of the deposits has been made by spectrophotometric analysis. The suspicion of a case of PVP-storage disease should result in a skin biopsy which usually is sufficient for the diagnosis.