A plant growing experiment was conducted in 2003-2004 on the aubergine cultivars ‘Epic’ F1 and ‘Solara’ F1 grown in an unheated polyethylene tunnel greenhouse at the Experimental Station in Marcelin, the University of Life Sciences in Poznań. The seedlings were planted on 15 May on beds at a 0.5×0.5 m spacing, i.e. 4 plants m–2, in 6 dm3 cylinders filled with substrate limed to pH H2O = 6.5, which consisted of: 1) highmoor peat from Lithuania, 2) pine bark from the pulp plant Zakłady Celulozowe + fen peat from Biskupice near Poznań (v : v = 1 : 1). The basic fertilization, i.e. pre-vegetation fertilization and top dressing with macronutrients, based on an analysis of the substrate was applied, using the universal method in 0.03 M CH3COOH. The fertilization was designed to achieve the following substrate abundance levels: L (N – 300, P – 265, K – 500 mg dm–3), S (N – 400, P – 350, K – 665 mg dm–3), H (N – 500, P – 440, K – 830 mg dm–3), while maintaining the N : P : K ratio as 1 : 0.9 : 1.7. The aim of this study has been to determine the effect of nitrogen, phosphorus and potassium on the content of macronutrients in fruits of two aubergine cultivars grown on organic substrates. The fruits were harvested in the first decade of August and underwent chemical analyses in order to determine concentrations of macroelement. For determination of the total forms of nutrients, the fruit samples were subjected to wet mineralization and the following nutrients were assayed: N, P, K, Ca, Mg. Significant differences between the cultivars were found only in the mean concentration of potassium, (‘Epic’ F1 – 26.65 g K kg–1 d.m, ‘Solara’ F1 – 29.72 g K kg–1 d.m) while the concentrations of nitrogen and calcium were significantly different between the substrate variants. No effect of the fertilization level on the mean content of nitrogen, phosphorus, potassium, magnesium or sulfur was found in aubergine fruits.