As the bridge stock in The Netherlands and Europe is ageing, various methods to analyze existing bridges are being studied. Load testing of bridges is an option to study the capacity when crucial information about the structure is lacking. This information could be related to the material (for example, the effect of ASR on the capacity) as well as to the structural system (for example, the effect of restraints at the supports or transverse redistribution capacity). When it is decided to load test a bridge, the question arises which maximum load should be attained during the experiment to approve the capacity of the bridge, and which criteria, based on the measurements during the test, would indicate that the test needs to be aborted before reaching the maximum desired load (the “stop criteria”). A number of reinforced concrete slab bridges have been load tested over the course of the past few years. These load tests were pilot cases, in which the bridges were heavily equipped with sensors, to study the bridges’ behavior at critical positions for bending moment and shear. The test results were then extensively analyzed, and compared to the stop criteria available in the currently used codes and guidelines. As a result of the analysis and experiments, recommendations are given for proof loading of bridges. These recommendations are important, since they will form the basis of a guideline for proof loading of existing concrete bridges that is under development in The Netherlands.