The presented research was conducted in order to determine the effect of hydrogen as an addition to the air-fuel mixture supplying a spark-ignition internal combustion engine. To carry out the tests, slight modifications were made to the engine structure, consisting in enabling the use of the necessary measuring equipment and adapting the engine to perform tests on the test stand. The applied modifications made it possible to measure the operating parameters generated by the engine, as well as to determine the composition of the emitted exhaust gases. The tests were carried out for a gasoline-powered engine, for a gasoline-powered engine using external exhaust gas recirculation (EGR) and for an engine fueled with gasoline with the addition of hydrogen and using external exhaust gas recirculation (EGR). In order to illustrate the results, they were summarized basing on a series of tests performed, and the effect of exhaust gas recirculation, hydrogen addition and a combination of exhaust gas recirculation and hydrogen addition on the performance and ecological parameters of the tested engine was determined. The conducted research and the obtained conclusions allowed for an unequivocal determination of the legitimacy of using hydrogen as a fuel additive for aconventional spark-ignition internal combustion engine in terms of utility and ecology.