1) 2-Thiouracil (2-TU) applied during low temperature treatment, inhibited flower formation in excised stem discs of Wedgwood iris. The inhibition was overcome by gibberellic acid (GA) and orotic acid but not by uracil or thymidine. 2) The first signs both of an inhibitive effect on flower initiation by 2-TU and of GA promotion occurred at the beginning of the reproductive stage. Increase or decrease of the rate of development of the flower primordium could be established only two weeks later, during differentiation of stamens or tepals. 3) The peak in respiration rate occurring in the bud at the beginning of the reproductive stage was entirely repressed by 2-TU and not restored on a medium containing 2-TU and GA. 4) It is concluded that a specific RNA takes part in the earlier stages of flower formation in Wedgwood iris. 5) The role of gibberellin-like substances in flower formation of the Wedgwood iris is discussed in the light of possible interaction with nucleic acid metabolism.