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The concept of varying pure-effects of nutrients on final yield, implying that all other growth factors are optimal relative to the concentration of the relevant nutrient, led to determination of reliable absolute and relative reference values for evaluating the nutritional status of young plants based on their chemical composition.The reference values were established from selected experimental data belonging to upper borderlines in the relationships between grain yield and concentrations of various nutrients in aerial parts of oats and spring wheat at fixed dry matter weight levels (DMw-levels).The selected data suggested definite absolutely optimal concentrations and varying relatively optimal concentrations of various nutrients, the latter dependent on the concentration of the 'pure'-effect nutrient.Absolutely and relatively optimal concentrations of various nutrients in young plants at fixed DMw-levels constitute the foundation for developing methods of diagnosis and prognosis.