**5. Aims**

The specific objective of the present in vivo study is to investigate chronobiological aspects of the status of acid-base balance and plasma ion concentrations in arterial blood (i.e., existence of possible circadian variations) and to determine whether there are differences between types of anesthesia after the immediate application of the most common anesthetics in in vivo rat experiments, pentobarbital (P), ketamine/xylazine (K/X), and zoletil (Z) in spontaneously breathing rats.
