This study evaluated serum concentration of intact parathormone (PTHi) in 30 dogs with chronic renal failure (CRF) (group 1) and in 40 healthy dogs (group 2), and correlated those levels with the serum calcium and phosphorus concentration. The median PTHi value for group 1 was 620.0 pg/mL. The median value for group 2 was 28.5 pg/mL. The mean serum value of corrected total calcium (cTCa) (correct calcium = total calcium - serum albumin + 3.5) for group 1 was 11.46mg/dL while group 2 showed a mean of 10.11 mg/dL Forty three % of group 1 presented with hypercalcemia and among these, 85% had high levels of PTHi, suggesting autonomous parathyroids. The mean serum levels of phosphorus in group 1 was 12.01 mg/dL. 4.33mg/dL was the mean in group 2. Hyperphosphatemia was present in 87% of group 1, and 96% of these dogs presented high PTHi; although 4 dogs of group 1 had normal phosphorus serum levels along with high serum PTHi, proving that phosphorus serum level is not enough for the diagnosis of hyperparathyroidism. A positive correlation was observed between phosphorus and PTHi for group 1 and no correlation was detected between calcium and PTHi. The evaluation of serum PTHi, calcium and phosphorus is important, and may help early diagnosis and better treatment of these dogs with CRF.