The main objective of this study was to examine age-associated changes in laboratory values in dogs in order to establish standard values for dogs of a certain age. These standard values could serve to judge the health status of individual dogs and possibly estimate their remaining life expectancy. Thus, haematological and immunological parameters, plasma constituents, kidney characteristics and the capacity of homeostasis were determined in German shephard dogs (0.5-13.5 years) and beagles (4-9 years). Significant changes were noted. We detected that the number of white blood cells declines with age. The change in a number of organ specific enzymes indicates organ involution and increased cell death. Increased plasma glucose levels and a decreased glucose tolerance point to a diminished sensitivity of tissue to concentrations change due to a decrease in organ production and changes in the immune system, which are also reflected in an impaired lymphocyte proliferation capacity. These factors lead to an increased blood sedimentation rate. Cortisol increases might reflect a reduced stress resistance. Age-related decreases in aldosterone concentration and PAH-clearance were also found.