Based on the assumption that latex production is positively correlated to the diameter of the latex vessels and hoping to obtain rubber plants with larger latex vessels than those observed in normal plants, the authors duplicated the chromosome number of small seedlings, using aqueous solutions of colchicine. Some polyploid plants with 72 chromosomes were obtained. A special technique was developed, ensuring the obtention of twin plants from a single seed, by splitting very young seedlings; one of them remained untreated, while the other was submitted to a colchicine aqueous solution. Any difference noted later between the plants could only be attributed to the treatment and in several cases chromosome doubling has been achieved. In this way the pair was constituted by a diploid (2n =36) and a tetraploid plant (2n =72). The results show that in the polyploid as compared to the normal plants the stomata are larger and in smaller number per area unit. Some morphological differences were also noticed. Up to now no measurements were taken of the latex vessels neither of the polyploids nor of the normal plants. The material was propagated by budding, and a large number of each developed clone is being included in field experiments to test their productivity and resistance to diseases.