The commercial value of Bacopa monnieri, a widespread herbaceous plant in Argentina, can be substantially improved increasing its flower size by chromosome doubling with colchicine. MS supplemented with 0.25 mg/L of 6-benzylaminopurine proved to be an appropriate medium for the in vitro multiplication of nodal segments of B. monnieri. Polyploidization was achieved submerging nodal segments during 24 or 48 hrs in colchicine solution 0.001 and 0.01 percent P/V, in 1 percent DMSO. Segments submerged in water and in DMSO 1 percent aqueous solution were used as controls. DNA contents from recovered plants was measured and characterized and their phenotype described. Two tetraploid plants originated from independent events were detected. These plants showed significant differences in size and colour both in leaves and flowers compared to untreated controls.