Submission of blood samples to referral laboratories is very common in veterinary practice. Internal reference ranges should take into account published ranges adapted to the methods and apparatus used and to the population under consideration. The aim of this study was to examine the results from 1022 consecutive canine blood tests, analysing the frequency and the main associations of abnormalities, and to compare the results in different age groups. Haemograms and serum biochemistry were compared with internal ranges and between age groups: younger than one year, one to eight years and older than eight years. Young dogs exhibited lower numbers of erythrocytes and lower values for haemoglobin concentration and packed cell volume. They also showed higher numbers of lymphocytes and higher concentrations of phosphorus and 71 per cent showed raised alkaline phosphatase. Neutrophilia, hypergammaglobulinaemia and hypoalbuminaemia occurred quite frequently in all dogs, and hypoalbuminaemia and hyperphosphataemia were commonly seen in uraemic patients. The simultaneous evaluation of cytolytic and hepatobiliary enzymes allowed better detection of liver damage, since only a very low percentage of dogs had simultaneous increases in all hepatic enzymes.