Loading tests are now seen as complementing structural analysis so that more reliable estimates of absolute stresses can be made. Testing of this kind is seen to be profitable, especially when a continuing programme justifies use of a special vehicles and modern electronic data gathering equipment. Three braod classes of test are identified; acceptance tests, assessment of load carrying capacity and research and development in support of design. Guidance on testing is presented. Success requires detailed definition of objectives, structural inspection, structural analysis and plans demonstrating that measured data will meet objectives despite adverse effects of ambient temperature changes and practical constrains on maximum loads, access and instrumentation