SummaryBeagle dogs continue to be used in experimental studies and preclinical and clinical trials, many of which address the usage of anaesthesia. In order to reduce the number of animals, researchers tend to conduct several experiments on a single animal. The question arises, however, as to whether or not this frequent usage involves more than simply additional stress and discomfort for the individual animal. Within the framework of an existing study involving six female Beagle dogs, we investigated the effects of repeated (5) isoflurane anaesthesia with xylazine/levomethadone/fenpipramide premedication carried out at short intervals (2 weeks) and compared these with the effects of two treatments intermitted by a longer resting period (8 weeks). To verify our hypothesis that frequent anaesthesia affects the dog's wellbeing more than the occasional anaesthesia, the following parameters were measured at regular intervals: body weight, body temperature, respiratory rate, blood pressure, reflexes and heart rate, both at rest and during a treadmill exercise. In addition, recovery behaviour subsequent to anaesthesia was monitored for one hour. Our observations indicate that the anaesthetic effects are most prominent 24 h after the anaesthetic treatment. However, crossover analysis of our data cannot show that there is no statistical difference of whether dogs were anaesthetized occasionally or frequently. In our study, it appears that frequent anaesthesia within a two-week period did not affect the wellbeing and general health of Beagle dogs in a super-additive manner and that a minimum of two-week testing-free period is sufficient to ensure complete recovery from the unwanted effects induced by anaesthesia.Keywords Repeated anaesthesia; isoflurane; premedication; Beagle dogs; animal welfare Beagle dogs continue to be used as laboratory animals in the development of new drugs or diagnostics, as well as for preclinical and clinical research. Complex questions and stressful or painful procedures often make it necessary to perform experiments under anaesthesia. In order to reduce the number of animals, researchers commonly conduct more than one experiment on the same animal. With regard to animal welfare, however, it needs to be ensured that the stress and discomfort for the single animal is not more than additive. To date, guidelines for anaesthesia in laboratory animals do not address the re-application of anaesthetics,