The Diagnosis and Recommendation Integrated System (DRIS) has previously been shown to be a valuable tool in making diagnoses of mineral imbalances in plants which, when corrected, result in yield increases. The basic tenets of this approach are discussed in relation to making diagnoses at high yield levels. Data for corn previously published in the literature are used to test the precision of the DRIS and critical value approaches. The results show that the DRIS approach is superior because it is capable of making valid diagnoses irrespective of crop age. It is also able to rank nutrients in their limiting order on crop yield which emphasizes the importance of nutrient balance in plant nutrition. The reason for the poorer performance of the critical value approach probably stems from the fact that the leaf tissue from which diagnoses is to be made, is not always taken at precisely the same physiological stage as was used in developing the norms.