The inability of potato buds to sprout due to dormancy constitutes a serious problem when the tuber is to be used as seed within short time from harvest. A number of chemicals have been used to break dormancy. Gibberellins are known to be the most effective chemicals for breaking potato dormancy. Moreover it is possibile that polyamines are also effective in breaking tubers dormancy, scince it was shown that before expiring potato tuber dormancy, the level of endogeneous gibberellins and polyamines will increase. Different studies have been recommended a wide range of gibberellin concentrations. But there is a few informations about applicatio of polyamines. This is particularly important for breaking minituber dormancy. Therefore two seprate experiments were carried out. Each experiment was conducted as factorial in a compeletly randomized design with 4 replications of 10 tubers. As the first experiment a 7×2×3 factorial experiment was conducted to examine the response of potato tubers to exogenous application of GA 3 (5, 10, 20 mg l -1 ) and spermine (30, 45, 60 mg l -1 ) with distilled water as control, cutting at the point of tuber attachment to the stolon and their interactions in terms of dormancy breaking and sprout growth of different cultivars (Agria, Marfona and Chandramukhi). Results showed that, in all cultivars, applying GA 3 or spermine advanced breaking of dormancy, but spermine was less effective. Applying GA 3 or spermine also increased the number of sprouts per tuber compaired with control. GA 3 treatments induced an increase in length of apical sprout, but spermine reduced it. Moreover there was strong interactions with cultivar and plant growth regulators in a way that, effects of these plant growth regulators were more clear in Chandramikhi. The diameter of apical sprout was significantly increased by spermine at the rate of 30 and 45 mg l -1 , but 10 and 20 mg l -1 GA 3 reduced it. No differences between cutted and not cutted tubers were observed regarding days to apical sprouting and length of apical sprout, but cutting at the point of attachment to the stolon reduced diameter of apical sprouts. A second 8×3 factorial experiment was carried out to examine the response of potato minitubers of different cultivars (Agria, Marfona and sante) to exogenous application of GA 3 (25, 50, 250 and 500 mg l -1 ) and spermine (60, 90, 120 mg l -1 ) and their interactions in terms of dormancy breaking and sprout growth. In this experiment, in all cultivars, applying GA 3 or spermine advanced breaking of dormancy, but spermine was less effective. Furthermore, applying GA 3 also increased the number of sprouts per minituber. The length of apical sprout
