The aim of this work was to examine the effect of altered carbohydrate composition on the carnation growth and development. A transgenic approach was applied in our experiments. Carnation leaves were transformed with modified mammalian bifunctional enzyme, coding 6-phosphofructo-2-kinase and fructose 2,6-bisphosphatase (6-PF-2-K/Fru-2,6-P2ase). This enzyme synthesizes and degrades the fructose 2,6-bisphosphate (Fru-2,6-P2) an important regulator of carbohydrate metabolism. Sucrose, starch, glucose and fructose content were influenced by modification of the Fru-2,6-P2 metabolite concentration. Differences could be observed in the morphology and the ontogeny of plants. The development of sucrose over-producing plants was faster than the starch accumulating and wild type ones.