As the first step to get historical background data for physiological examinations in juvenile dogs, hematology and blood chemistry data obtained from juvenile beagle dogs (less than 3 months of age) used in the control group of toxicity studies conducted in our laboratory were summarized and compared with those obtained from adult beagle dogs (6 months of age). In the hematological examination, growth of beagle dogs was shown to be associated with increases in erythrocyte parameters and with decreases in reticulocyte and leukocyte counts. In the blood chemical examination, growth of beagle dogs was shown to be associated with increases in aspartate aminotransferase, alanine aminotransferase, and creatinine and with decreases in creatine phosphokinase, glucose, total cholesterol, and calcium. The differential leukocyte ratio showed no age relation, but the actual count showed a tendency toward decrease. Alkaline phosphatase showed a tendency to increase from 0 months of age to 3 months of age, but it decreased at 6 months of age. The present results were roughly similar to those previously reported.