Three onion cultivars viz. Renate, Ailsa Craig and SS1 were characterised according to their mineral content. The concentrations of the macronutrients phosphorus, potassium, calcium, manganese and sulphur and the micronutrients iron, boron, manganese, copper and zinc were analysed in freshly harvested and stored onion bulbs using ICP-AES (Inductively coupled plasma-atomic emission spectroscopy). Onions were treated pre-harvest with additional sulphur (100 kg ha−1) and/or calcium (300 kg ha−1) applied in four combinations at the time of seed drilling, however these treatments did not affect the total concentrations of sulphur or calcium in the harvested bulbs. The data were subjected to canonical variate analysis in order to determine the most appropriate variate to discriminate between cultivars. Two canonical variates were sufficient to differentiate between the three cultivars, with the first canonical variate describing differences in micronutrients between the genotypes and the second separating the cultivars by differences in sulphur concentration.