The inter-relationships between the leaf contents of 4 major nutrients, nitrogen, calcium, magnesium and potassium, are discussed within the context of a nutrient-element balance in citrus leaves. It was found that there was an unequal 3-way competition between the cations, potassium being perhaps the strongest antagonist of the three bases. There was also a reciprocative relationship between nitrogen and calcium, the data so far suggests a one-way phenomenon in favour of calcium. Furthermore the nitrogen/calcium ratio appears to have a significant effect on the leaf content of potassium, but not on the leaf content of magnesium.