the leading cause of permanent disability in the developed countries. Yet there is no effective treatment available for the majority of stroke patients. Currently there are no in vitro methods that could satisfactorily simulate the complex interplay of vasculature, brain tissue, and blood during stroke, and thus could replace the greater part of animal experiments. During animal experimentation the following prerequisites have to be fulfilled to maintain the ethical justification (“the three Rs”): Reduction: Animal numbers have to be kept as little as possible (but as high as necessary - to avoid underpowered studies -) to draw scientific conclusions. Refinement: Experiments have to be best planned and to be conducted by trained personnel to minimize the suffering of animals on the one hand and to gain as much knowledge as possible out of the utilized animals. Replacement: Whenever possible animal experiments have to be replaced by other methods (e.g. cell culture, computed simulations etc.). References Stroke Stroke