Plasma components of 6 to 12-month-old beagles were examined using a Technicon auto-analyzer. Age-related changes were noted for 8 of the 21 components: the levels of total protein (T. Pro) and iron (Fe) gradually increased while those of alkaline phosphatase (ALP), creatine phosphokinase (CPK) and inorganic phosphorus (Pi) persistently decreased in both sexes. Triglyceride (Trigly) in female dogs, glutamic-pyruvic transaminase (GPT) and urea nitrogen (Urea-N) in male dogs tended to increase. The following thirteen components showed no significant variation during the period of observation: glucose (Glu), lactic dehydrogenase (LDH), albumin (Alb), creatinine (Crea), glutamic-oxaloacetic transaminase (GOT), leucine aminopeptidase (LAP), total bilirubin (T. Bil), amylase (Amy), total cholesterol (T. Chol), sodium (Na), potassium (K), chloride (Cl) and calcium (Ca). Our results generally agree with the reported findings on beagles from various institutions.