Improvements of working conditions in plasma-jet spectrometry are described and an internal standard method and background compensation method are proposed in order to reduce the fluctuation of analytical curves for magnesium and calcium. In addition, examinations were made of effects of coexisting elements, and determinations of calcium and magnesium in iron ores and of calcium in cast irons were carried out. In this method, the relative standard deviation is 4·5 per cent for 0·0152 per cent of calcium in cast iron.