In agricultural practice, there is a need to change the forms of fertilizers to be friendlier to the natural environment and human health. To this end, research has been carried out on the partial replacement of fertilisers containing nitrates or ammonium compounds with amino acid nitrogen. The present studies assessed the effect of L-glycine on growth parameters and on the content of selected nutrients in the butterhead lettuce grown in an unheated greenhouse in the spring. The treatment consisted of foliar L-glycine application at the following concentrations: 0, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 220 and 240 mg∙L-1, with a solution dose of 50 ml∙m-2. Foliar application of L-glycine improved the butterhead lettuce growth parameters. The most favourable values of the head weight, root system weight and the number and length of leaves were recorded for the plants fed with doses ranging from 80 to 120 mg∙L-1. The weight of the head and the root system was most favourable after foliar feeding with 120 mg∙L-1 of L-glycine. Additionally, a high value of the SPAD leaf greenness index was noted as a response to the same dose, indicating a high level of leaf nitrogen nutrition. However, foliar feeding with L-glycine had no statistically significant effect on the nutritional value of lettuce, i.e. the content of dry matter, protein, sugars and ascorbic acid.