The effect of hydrogen gas on the plasma and its influence on acid interferences in plasma atomic emission spectrometry was studied. The study was performed with HCl and HNO3 in the concentration range of 0 /2 mol l 1. Vanadium and magnesium were used as test elements, the study was extended to other several elements. The effects of hydrogen gas on the plasma were studied by measuring excitation temperature, electron number density and the ionicto- atomic line intensity ratio. The net effect of hydrogen was an increase in electron density and ionic to atomic line intensity ratio. A small increase in the excitation temperature was observed. The signal suppression for ionic lines causes by mineral acid was reduced when small amounts of hydrogen was introduced into the plasma as sheathing gas. This effect was attributed to the increase in plasma electron density.