The relationships between total serum calcium and serum albumin and total serum calcium and serum protein concentrations were examined in 291 cats. There was a significant (P less than 0.001) linear relationship between serum calcium and serum albumin concentrations. Because of extreme variability among the calcium and albumin concentrations (R2 = 0.18), however, a dependable formula to adjust total serum calcium values for albumin or protein binding in the cat could not be constructed. An adjustment formula could not be based on the relationship between calcium and total protein concentrations because of the lack of a significant relationship (P = 0.21). The association between serum calcium and serum albumin or serum calcium and total protein concentrations is weaker in cats than in dogs or man.