Chronic renal failure (CRF) causes immunosuppresion in humans and is thought to be one of the causes of noninfectious secondary immunosuppression in dogs. Hematological, biochemical, and immunological examinations were performed on blood samples obtained from dogs in various stages of CRF. The number of dogs with lymphopenia increased with the progression of clinical signs. All main subsets of lymphocytes were decreased, but more considerable reduction was detected in B-cells, Tc-cells, and NK cells. Depressed lymphocyte response to concanavalin A and pokeweed mitogen was found in dogs with severe clinical signs and lymphopenia. Our results, showing impaired immunological functions, are similar to results obtained from uremic humans, suggesting that infection may be an important complication in dogs with CRF.