The presence and distribution of anionic sites in the glomerular basement membrane and visceral epithelial cell coat has been demonstrated. No definite decrease in intensity or periodicity of staining of basement membrane particulate sites was seen in protein overload proteinuric animals and only one staining technique employed for electron microscopy (alcian blue 8GX) demonstrated a focal decrease in visceral epithelial cell coat staining in severely damaged glomeruli. A decrease in overall glomerular staining was also demonstrated by quantitative analysis of colloidal iron staining by light microscopy. The findings differ from those described in puromycin aminonucleoside nephropathy and nephrotoxic nephritis. Staining was demonstrated also in other basement membranes, in Bowman's capsule and along interstitial collagen fibres.