A suppression subtractive hybridization approach (SSH) was used to generate a cDNA library enriched in clones representing genes that are up-regulated in the potato tuber apical bud on dormancy release. The sequences of cDNAs representing 385 different genes were determined. This study focuses on the characterization of one of these cDNAs. On the basis of sequence similarity, the cDNA was identified as encoding a member of the auxin response factor family (ARF6). The expression pattern of potato ARF6 was determined by in situ hybridization. In apical tuber buds in the early stages of sprouting, relatively high levels of ARF6-specific transcripts were detected, especially in the peripheral zones of the tunica and corpus of the apical meristems. Expression was also detected in procambial and early vascular tissues, both subtending the meristem and in adjacent leaf primordia. By contrast, in dormant buds no expression of ARF6 could be detected. The expression pattern was also determined during the tuberization process; steady-state expression levels decreased c. 10-fold in the apical region as tuberization proceeded. In non-growing buds, exhibiting correlative inhibition, ARF6-specific transcript levels were relatively low, but rapidly increased when apical dominance was removed by excision of the apical bud. The effects of gibberellin and auxin on axillary bud growth and ARF6 expression are described.