Unreduced gametes are the driving force for the polyploidization of plants in nature, and are also an important tool for ploidy breeding. In present study the occurrence and behaviour of unreduced pollen as well as the possibilities to induce this phenomenon in Begonia was studied. The natural presence of unreduced pollen is not a rare phenomenon in Begonia. In ten of the 70 screened genotypes large pollen were observed with a rather spherical than normal ellipsoidal shape. Flow cytometric data proved that these aberrantly shaped pollen were associated with 2n ploidy levels, although they were not always viable. Also frequencies varied significantly between genotypes. The most reliable results were obtained after nuclei isolation from germinated pollen followed by flow cytometric analysis. All 2n pollen producers showed a mechanism equivalent to first division restitution (FDR), in which chromosomes did not segregate during meiosis I but only during meiosis II.. Different treatments to induce unreduced pollen formation among others temperature stress, trifluralin and N2O treatments were tested. Especially with N2O treatment induction of fertile unreduced pollen was obtained in sterile hybrids. Inheritance of 2n pollen formation was investigated in F1 and F2 progenies of B. ‘Orococo’ by analysing the microsporogenesis and pollen size, which is correlated to the ploidy level. The results show that the inheritance of 2n pollen is very high and is probably modulated by one dominant gene and some modifier genes.