For many decades, conducting biological experiments on laboratory animals was part of diagnosing infectious diseases of both animals and humans in laboratories. The same practice was applied at our institute. Built 50 years ago, the initial animal facility at SVI Prague was redesigned and refurbished in the late 1990s and, subsequently, received accreditation. The facility once consisted of a breeding section and an experimental section. The former was discontinued in the past; the number of approved species was very recently reduced along with the number of individual authorised experiments. The diagnosis of infectious diseases remains the sole aim of biological experimenting at SVI Prague. In accordance with the application of the “3R” rule (replacement, reduction, refinement) we have managed to reduce and replace some of the biological experiments. Thanks to the introduction of molecular methods, the number of experiments has been gradually minimised and, thereby, also the total number of individuals used in the experiments. In each of the experiment, the number of animals is reduced to a minimum permitting the results of the testing to be evaluated. Despite all the advances in the field of diagnosing infectious diseases, it is not yet possible to replace the two latest authorised biological experiments with adequate diagnostic methods