The protein fractions in urine from proteinuric dogs with and without pyoderma were estimated. Fifteen dogs with pyoderma (five with superficial and 10 with deep pyoderma) were compared with 10 dogs with glomerulopathy and 27 dogs with diseases other than pyoderma or urinary tract problems. Agarose gel electrophoresis was used to fractionate the proteins. Three types of electrophoretogram were obtained with albuminuria, globulinuria and serum-like profiles. An albuminuria profile was found in eight of the 27 dogs with other diseases, in three of the five dogs with superficial pyoderma, in eight of the 10 dogs with deep pyoderma and in all 10 dogs with glomerulopathy. The albuminuria profile (mean [sem] albumin/globulin ratio 1·98 [0·10]) was also characterised by α_1b, α_2a and β₂ globulin peaks in all 29 dogs with this profile, which was therefore thought to indicate that albuminuria (glomerular proteinuria) was a result of glomerular damage and inflammation because α_1b, α_2a and β₂ globulins are considered to be acute phase proteins. The serum-like profile (mean [sem] albumin/globulin ratio 0·72 [0·01]) was observed in 13 per cent of the proteinuric dogs examined and contained all the protein fractions normally detected by electrophoresis of serum. The profile was considered to be a variant form of the albuminuria profile, probably indicating advanced glomerular lesions and inflammation. The globulinuria profile (mean [sem] albumin/globulin ratio 0·33 [0·08]) was signifi- cantly different from the other two in that it was characterised by a low albumin peak and the presence of globulin fractions not clearly distinguishable from each other because of their confluency and absence of individual peaks. This profile could indicate severe glomerulotubular lesions and degradation of certain protein fractions. It could also be a result of increased secretion of tissue and other proteins by damaged tubules. It was concluded that glomerular damage leads to glomerular proteinuria characterised by high proportions of albumin together with α_1b, α_2a and β₂ globulins in lower but significantly diagnostic proportions.