To study dietary management of chronic renal failure (CRF), 1.600 dogs older than 5 years were screened for serum urea and creatinine concentration. 358 dogs (22.4 %) showed values above normal (6.67 mmol/l of serum urea, 106 mu mol/l of serum creatinine). Sixty of these dogs with slight or moderate clinical signs of CRF were selected for the study. Thirty-two dogs were fed a commercial canned medium protein diet (MPD; 27 % protein, 0.36 % phosphorus in dry matter) and 28 dogs were fed a home made diet (HMD; 21.5 % protein, 0.38 % phosphorus). Dogs were reevaluated for clinical status, blood chemistry profile and urinalysis at 9 intervals over 28 weeks. In general, palatability of both diets was high and dogs maintained their body weight. Nevertheless 8 dogs of the MPD and 6 dogs of the HMD group died or had to be euthanized during the study. In surviving dogs serum urea, creatinine, phosphorus and (Ca x P) were significantly reduced nearly to the normal range after 4 weeks. A slight increase at the end of the study occured because clients did not adhere strictly to dietary instructions after recovery of the dogs. These results suggest that elderly dogs frequently show a mild to moderate CRF, and dietary treatment with medium protein and low phosphorus diets is effective in improving blood chemistry data as well as physical condition of those dogs. Efficacy of medium protein diets in canine chronic renal failure was the same in a small animal clinic, compliance of dog owners was not sufficient for long term management.