The enhancement of chilling tolerance in leaves of different age in cucumber (Cucumis sativus L.) and wheat (Triticum aestevum L.) plants treated by a daily short-term temperature drop was studied. Plants were subjected to short-term (2 h at the end of the night)temperature drops to 12°C (cucumber) or 4 °C (wheat) for 6 days in the phase of the actively growing first (wheat) or true second (cucumber) leaf (DROP1) or growth-completing, i. e. mature first or second leaf, respectively (DROP2). DROP3 plants were treated by DROP throughout the first or second leaf growth period (12 days). The leaf cold tolerance was assessed by the resistance of leaf cells to short-term freezing. Cell membrane permeability was estimated by relative electrolyte leakage. Both young and mature leaves responded to DROP treatments by enhanced leaf cold tolerance, but in mature leaves that have completed their growth, cold tolerance was higher than in young, actively growing leaves. Relative electrolyte leakage from tissues of mature leaves was lower than from young leaves, which testifies to higher membrane stability of mature DROP-treated leaves. It is hypothesized that the differences detected in the tolerance of DROP-treated leaves of different age are associated with their structural (anatomical-morphological) and metabolic features.