In order to obtain a clear picture of the deficiency and toxicity symptoms of boron, young Eucalyptus grandis plants were grown in nutrient solution in the absence and increasing levels of B (0; 0,125; 0.500; 1.000; 2.000 and 4.000 ppm). Chemical analysis were run for N, P, K, Ca, Mg, B, Cu, Fe, Mn and Zn in order to discover any interference of boron. The symptoms of malnutrition of boron were easily identified. Symptoms of boron toxicity were uncertain. Practically, no interference of boron on the other nutrients was observed. Malnutrition symptoms were associated with a concentration of 46 ppm of boron in the young leaves. Toxicity became visible with 100 ppm of boron in the mature leaves. The "critical level" fitted with 61 ppm of boron in the young leaves.