The serum concentrations of haptoglobin, caeruloplasmin, C-reactive protein and serum amyloid A were measured in three groups of seven healthy dogs. Group 1 received a single dose of 1.1 mg/kg methylprednisolone acetate, administered subcutaneously; group 2 received 1 mg/kg per day of prednisone administered orally for three weeks; and group 3 received 2.2 mg/kg per day of prednisone administered orally for seven days. Before the administration of the glucocorticoids the serum concentrations of all the acute phase proteins were within the authors' laboratory reference ranges. After the administration of the drugs there were significant increases in the concentration of haptoglobin in all three groups, the increases being larger in groups 2 and 3. In contrast, the concentrations of C-reactive protein, caeruloplasmin and serum amyloid A were not affected.