The normal ranges for a variety of hematologic and clinical chemistry findings in 1,540 control BALB/c and C57BL/6 mice of various ages was determined. The total leukocyte count for both strains was highest at 1-3 months of age, and it usually decreased slightly until the mice were 18 months old. Hemoglobin values decreased with age. In both strains, the values for phosphorous, calcium, alkaline phosphatase, and urea nitrogen decreased after 3 months of age and then increased after 12 months of age. Differences between sexes were present for one or both of the strains for hemoglobin, phosphorus, glucose, cholesterol, aspartate aminotransferase, total protein, albumin, and alkaline phosphatase.