Foliar discs (8 mm diameter) from expanding leaves of the middle part of vegetative shoots of Chrysanthemum morifolium Ramat raised in vitro, rooted on their basal side from the 6th day when cultured in vitro on a Murashige and Skoog medium containing indolylacetic acid (1 mg/l). Measurements (every two days) of free putrescine indicated a continuous level increase from the beginning. Conjugated polyamines (75% in the hydroxycinnamoyl form) raised from zero at the beginning of culture to peak at day 4. No ODC (ornithine decarboxylase) or ADC (arginine decarboxylase) activity was detected at day 0 but a high activity of both enzymes was measured at day 2 (ODC > ADC); it declined afterwards. DFMA (α-difluoromethylarginine), an inhibitor of ADC, when incorporated in the rooting medium from time 0 (10⁻³ M), inhibited completely ADC activity, but reduced the level of free putrescine by only 25% in the leaf explants without affecting the conjugated pool, and it had no effect on rooting. DFMO ( α-difluoromethylornithine ), an inhibitor of ODC at the same concentration, completely inhibited ODC activity with a reduction of putrescine accumulation and a total inhibition of the formation of polyamine conjugates. Root formation was totally inhibited by DFMO alone. A simultaneous application of putrescine (10⁻³ M) to DFMO restored complete rooting. There was no DAO (diamine oxidase) activity at day 0 in the foliar explants but it increased rapidly to a maximum at day 2 on the rooting medium. PAO (polyamine oxidase) activity did not undergo such a variation. No DAO activity was measured in explants on the root- non forming medium containing DFMO. β-OH hydrazine, an inhibitor of DAO, inhibited the development of activity of this enzyme in the leaf explants on the rooting medium. Putrescine and its conjugate accumulated in such treated explants. Rooting was completely inhibited in the presence of β-OH hydrazine but callus grew around the disc. Such a callus did not develop in the presence of DFMO. The results thus pointed to the involvement of ODC-mediated biosynthesis and DAO-mediated catabolism of putrescine in the induction of rooting of this material.