A hydroponic experiment has been conducted to determine the physiological and biochemical response of four new rye lines – S120, S76, OT1-3 and 541 – bred at the Department of Plant Genetics and Breeding, Agricultural University in Szczecin. Seeds were sown into soil and placed into a phytotrone chamber with controlled atmosphere and photoperiod. The relative humidity was 80%, the temperature maintained at 20ºC and the intensity of photosynthetically active radiation (Phar) was 700 μmol⋅m-2⋅s-1. Seed germination occurred after about 5 days. The seeds were characterised by different germination ability: 80% for S120, 100% for S76, 82% in OT1, and just 50% for 541 line. Rye seedlings, at the 2-3 leaf stage, were placed in hydroponic units and a two-factor experiment was set up, with potassium deficiency being the first factor and rye lines the second one. The control variant consisted of seedlings placed on complete Hoagland’s medium, while potassium starvation was performed on a medium with 50% deficiency of this element. After seven days, fresh matter was weighed, proline content was measured according to the BATES method (1973) and amounts assimilation pigments were measured according to the method of ARNON et al. (1956). The results were processed statistically, performing a two-factor analysis of variance, while the significance of factors was tested using Tukey’s test at α = 0.05. The study aimed at examining selected physiological and biochemical indicators of the resistance response of four rye lines to stress induced by potassium deficiency. Application of 50% potassium deficiency in a medium induced an increase in the content of assimilation pigments in leaf fresh matter of S120 rye line. A correlation was found between proline content and that of assimilation pigments. The largest proline quantity, 27.2 μg⋅g-1 f.m., was found in 541 rye line seedlings, but its content decreased together with fresh matter yield. It was also found that the total chlorophyll content was directly proportional to the content of proline in S120, S76 and OT1-3 rye lines, whereas in the case of other pigments such a relationship existed only for S 120 and S76 rye lines.