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The increasing use of pressure die cast magnesium alloys for the manufactur-ing of automotive components requires materials values, which describe completely the mechanical behaviour. Present, there is a lack of data, especially for the design process of safety relevant components. Therefore, fracture mechanics investigations were carried out to assess the crack resistance of the alloys AZ91, AM50 and AE42 on the basis of the mul-tispecimen test method. The investigations occurred on SENB- and CT-specimens taken from plate-like components of the same dimensions.The results clearly reveal the correlation between crack resistance and microstructure concerning mainly the influence of the concentration and distribution of intermetallic phases. Because of the cast-induced defects like microshrinkage and gas inclusion the good intrinsic properties of the alloys are not exploited.