Examinations of exhaust gas aftertreatment systems fitted to internal combustion engines allow for validation, evaluation and development of the assemblies under test. Measurements of exhaust gas composition are carried out using measuring equipment of the highest quality. It is possible to measure concentrations of gaseous exhaust gas components such as THC (total hydrocarbons), CH4 (methane), NOx, NO, NO2 (nitrogen oxides), CO (carbon monoxide), CO2 (carbon dioxide), O2 (oxygen), NH3 (ammonia) and N2O (nitrous oxide). The quantity of solid particles is determined by measuring the mass of particles (PM), the number of particles (PN), the particle size distribution, and the opacity and emission opacity of the exhaust gas. The measurements of the efficiency of the exhaust aftertreatment system may be carried out in accordance with standardised approval procedures, as well as procedures determined individually for the purposes of the test. Catalytic reactors and filters can be subjected to durability and ageing tests, the purpose of which is to determine the viability or development direction of the test system.