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A positive linear relationship was found between total calcium and albumin and between total calcium and total protein in the serum of 209 dogs. Total calcium concentration correlated with the concentration of albumin (r = 0.575; P less than 0.001) and with the concentration of total protein (r = 0.411; P less than 0.001). A correction formula for calcium was derived on the basis of the concentration of albumin: adjusted calcium (mg/dl) = calcium (mg/dl) - albumin (g/dl) + 3.5. The correction formula for calcium, based on the concentration of serum total protein was: adjusted calcium (mg/dl) = calcium (mg/dl) - 0.4 [total serum protein (g/dl)] + 3.3. Hypocalcemia (less than or equal to 8.7 mg/dl) was detected in 32 of the dogs. After adjustment of the measured total calcium for albumin and serum total protein, 29 (91%) of the dogs had calcium concentrations within the normal range. Hypercalcemia was not associated with hyperalbuminemia or hyperproteinemia. In 91% of dogs with disorders of calcium metabolism and in 86% of dogs less than 6 months old, calcium concentrations were outside the 95% confidence intervals for albumin and total protein calculated from the 209 dogs. It was concluded that adjustment of serum total calcium for protein concentration is essential for correct interpretation of calcium values and detection of abnormalities in calcium metabolism.