Chronic renal failure was diagnosed in 15 Bull terrier dogs. The dogs ranged in age from one to 8 years. History and clinical findings typically included lethargy, anorexia, polyuria, polydipsia and weight loss. Affected dogs were azotaemic, had elevated serum phosphate and cholesterol, and proteinuria was apparent in all dogs tested (13/13). The concentration of urine was consistently in the nil to minimally concentrated range (specific gravities 1.011-1.017). In those dogs necropsied, both kidneys were approximately two-thirds normal size, tough in consistency, with a pale cortex and a finely nodular capsular surface. Histologically, there was marked nephron loss, diffuse interstitial fibrosis and focal dense radial fibrosis which was especially evident in the renal medulla. Tubular dilation was widespread with focal mineralisation of tubular epithelium and adjacent basement membranes. Glomeruli were often shrunken and segmentally fibrotic. Some Bowman's spaces were extremely dilated. Many less severely affected glomeruli had thickened basement membranes.