Reference biochemical ranges for young adult and adult ewes in mid-gestation were derived from 83 pooled serum samples taken from 30 flocks in the Province of Québec, Canada. In each flock the samples were pooled into three age categories and each category contained between six and 10 samples. The blood samples were taken by jugular venepuncture in December 1999. All the values were within the normal published ranges. As the age of the ewes increased there were slight increases in the concentrations of globulin and total protein and decreases in the concentrations of calcium, phosphorus, creatinine, glucose and albumin, and in the activities of alkaline phosphatase and glutathione peroxidase.