The effect of sodium 2,3-dichloroisobutyrate (DCIB-Na) was studied as exerted on the tuberization of potatoes under in vitro conditions. DCIB-Na was applied to 25 days old plants at rates of 0, 50, 100, 200 and 400 mg per litre, together with an 8 % solution of saccharose. A low DCIB-Na application rate inhibited tuber formation (by 30%) and a high dose had no adverse effect on tuber number and ... [Show full abstract] size. The optimum application rates were 100 and 200 mg of the substance per 1 litre of the medium: these doses provided a significant increase of the average weight of the microtubers (by 46 to 55 %) and of the total weight of the tubers in the culture container (by 38 to 57%). The studied inhibitor appears to show an antigibberellin reaction and to increase the rate of tuber initiation. DCIB-Na can be recommended to be used in in vitro tuberization of potatoes.