In this study, the influence of hydrogen content, melt cleanliness and solidification conditions on the porosity distribution and mechanical properties have been investigated in a laboratory scale step mould casting with an A356 alloy. Three hydrogen levels, namely 0.10, 0.20 and 0.40 mL/100 g, were reached by treatment of the melt by Ar degassing, Ar-10H(2) and Ar water vapour mixture respectively. The hydrogen content of the melt was continuously measured. For each hydrogen level, two castings were produced, namely with and without filter. Porosity was increased with increasing hydrogen content but there was no significant effect of filtration. Moreover, similar tensile properties were achieved with different hydrogen levels and different porosity levels.