The paper presents the results of the research on lettuce yielding and its chemical composition as dependent on ammonium nitrate and calcium carbonate doses. The experiment with lettuce cv. Omega was carried out in a greenhouse, in 2 litre pots, filled with transition peat, with liming in accordance with the experimental design. After the completion of the experiment, the substrate indicated a high content of calcium (1722, 2963, 4445 mg Ca dm-3). In objects with higher content of calcium an increase was observed in mineral nitrogen concentration, and a decrease of phosphorus and potassium. EC value was higher when the substrate had a higher content of mineral nitrogen and potassium. On the other hand, calcium did not influence that value. Yield of lettuce was formed first of all under the influence of nitrogen fertilisation. Taking into account the yield and nitrogen content in leaves, mineral nitrogen concentration in substrate in lettuce cultivation should not be higher than 180-200 mg N-NH4+N-NO3 dm-3. Content of calcium in lettuce leaves underwent slight changes, from 0.8 to 1.3% d.m. Lettuce leaves were healthy and no tipburn was noted, irrespective of the content in substrate and leaves.