S-adenosylmethionine decarboxylase (SAMDC; EC 22.214.171.124) is a key regulatory enzyme in the polyamine biosynthetic pathway. Numerous studies have shown that the enzyme activity and polyamine levels are generally correlated with cellular growth in plants, animals and bacteria. In order to gain more insight into the role of polyamines in plants, human SAMDC cDNA under control of 35S promoter of cauliflower mosaic virus, along with a neomycin phosphotransferase gene, was transferred to tobacco (Nicotiana tabacum cv.Xanthi) via Agrobacterium tumefaciens. Transgenic plants showed the presence of SAMDC mRNA and a 2-4-fold increase in SAMDC activity. In the transformed tissues, putrescine levels were significantly reduced, while spermidine content was 2-3 times higher than the control tissues. Cellular spermine content was either increased or remained unchanged. Excised leaf segments from transformed plants frequently produced shoots even on callus inducing medium.