Within the context of reducing the green house gas emissions, substituting hydrogen for natural gas could have a great environmental impact, but hydrogen has different combustion characteristics than natural gas. This paper reports results of experimental tests of premixed combustion of natural gas-hydrogen mixtures in a porous burner made of open cell metallic foam. The technology of porous radiant burners shows environmental and economical advantages compared to traditional diffusion flame burners. The tests showed that substituting natural gas for hydrogen in a porous burner reduces the pollutant emissions of CO and NOx and the quantity of CO2 produced. For specific powers below 500 kW/m2, the emissions were below the "Blue Angel" label values. But working conditions are limited by hydrogen addition and the equivalence ratio has to be lowered to prevent flashback. The radiant combustion mode is more difficult to obtain with mixtures containing hydrogen and it disappears completely for mixtures with more than 80% vol. hydrogen.