The stay cable system of the Rędziński Bridge in Wrocław, the largest concrete bridge in Poland, was the subject of dynamic investigation carried out within the international research project “Dynamic monitoring of bridge structures”. Dynamic measurements and the Structural Health Monitoring system of the bridge were used for the purpose of this research. The aim of the analysis was to determine the tension forces of the stay cables by using the indirect method of measurements and to compare the results with the data directly imported from the bridge monitoring system. 20 monitored stay cables were selected for dynamic investigation. In general, the values of tension forces determined by dynamic methods were higher than those from the monitoring system. This intriguing fact may be connected with the necessity to calibrate the force sensors installed in the stay cables. Some of the force sensors in the SHM system are inactive (no measurement data available) and definitely need to be replaced. In this paper, the results of measurements, discussion and interpretation of obtained data are presented.