The aim of the study was to determine whether birds of different breeds, with different preferences for environmental elements and kept in identical conditions, would exhibit different behaviour and stress levels. The research material consisted of 50 laying hens of the Green-legged partridge (Zk), Polbar (Pb), and Leghorn (Lg) breeds. The birds were provided with identical environmental conditions. They were kept on litter in separate boxes, with 25 individuals of one breed per box, in the same building. An open field test was used in determining the behaviour of the birds. Levels of cortisol in serum and corticosterone in feathers were evaluated, and haematological and biochemical analyses of blood were performed. Leghorns proved to be a highly excitable and active breed whose needs cannot be fully satisfied in the standard conditions of large farms. Based on a differential leukocyte count, their hyperactivity was associated with increased stress. The Green-legged partridge exhibited the lowest stress levels. Birds kept in the same environmental conditions were found to differ significantly in the level of stress, probably because of differences in their behavioural needs and the possibilities of satisfying them. To reduce stress levels and improve the welfare of hens, it is necessary to verify their preferences first. Stress indicators are elevated in highly excitable birds, and the conditions on large farms are not conducive to meeting their behavioural needs.