Determination of plant analysis criteria characterizing the magnesium nutrition of oats, spring wheat and maizeCereal plants from pot trials were analyzed for criteria of optimal Mg nutrition. The critical Mg concentration in dry matter of aerial parts fromoatsandspring wheatat the beginning of the shooting stage was found to be 1.8 and 1.3 per mille Mg respectively. The critical Mg concentration withmaizeis about 2,2 per mille in dry matter of yount leaves at tasseling stage.Because the Mg content of oats (based on dry matter) decreases significantly during the shooting stage, it seems advisable to have additional data (Mg content of green matter, Mg/N ratio, Mg/Ca ratio) which are less influenced by plant age.The Mg/Ca ratio appears to be well suited for evaluating the nutritional status of cereals. Minimum critical Mg/Ca ratios (based on per mille contents) are 0,23 for spring wheat, 0.3 for oats and 0.4 for maize.