Abstract. Laboratory experiments were conducted to study the effect of soil drought on leaf gas exchange and water relations of young sunflower plants (Helianthus annuus L.) – cv. Favorit and cv. Albena. Similar changes were established in the parameters tested. Significant inhibition of net photosynthetic rate, transpiration intensity and stomatal conductance were observed. Cultivar’s differences were also established, particularly marked in terms of transpiration intensity and stomatal conductance, which were more strongly inhibited in plants of cv. Favorit. Among the water exchange parameters, it was the leaf water potential (Ψ) that changed most in both cultivars, becoming more than two times lower.