Effects of treatments with gibberellic acid (GA(3), 50 mg L-1 for 2 h) or carbon disulphide (CS2, 25 ml m(-3) for four days) on breaking of dormancy and sprouting of potato (Solanum tuberosum L., cvs Agria and Marfona) minitubers of different weight classes (0.3, 0.7 and 1.5 g) were investigated. The dormancy period tended to decrease with an increase in the weight of minitubers, whereas the number of sprouts per minituber, their length and fresh weight and the sprout mass per unit of sprout length of the longest sprout tended to increase with an increase in minituber weight. In both cultivars, applying GA(3) or CS2 advanced breaking of dormancy, but GA(3) was less effective in Marfona than in Agria. Advancing breaking of dormancy was associated with removal of apical dominance and therefore applying GA(3) or CS2 also increased the number of sprouts per minituber, especially in Agria. In Agria, the dry matter content of sprouts from the CS2 treatment was higher than in the GA(3) or control treatments, whereas in Marfona dry matter content of sprouts was highest in the GA(3) treatment. The length of sprouts, fresh weight of sprouts and the sprout mass per unit of sprout length of the longest sprout were significantly enhanced by treating minitubers with GA(3) or CS2 compared with the untreated control minitubers, but there were strong interactions with cultivar and minituber weight. These interactions are important in practical use of dormancy breaking methods. (C) 2009 Elsevier B.V. All rights reserved.