During an extensive investigation of some 25 concrete bridges and other structures suffering from alkali-silica reaction it has been found that the uniaxial tensile strength of the concrete was extremely low in relation to both the compressive strength and the splitting tensile strength. It is known that concrete with damage due to ASR has reduced mechanical properties. The literature indicates that with an expansion of 1 0/00 a reduction of 30 % may occur. The reduction found in some of the bridges was, however, up to 82 % with an expansion between 0.5 and 1.0 0/00. There was no clear reduction of the tensile splitting strength and the compressive strength. Previous research on older concrete structures without ASR showed that low tensile strength is not exclusively connected to the presence of ASR. Although not conclusive, Petrographic Fluorescence Microscopy (PFM) research and visual inspection of the structural damage of the concrete structures with ASR indicate that at least part of the damage must be due to ASR. The structural damage due to ASR and due to other causes cannot be distinguished.