It had been obtained a tetraploid hybrid (2n=40), crossing Z. diploperennis (2n=20) with Z. perennis (2n=40) by non disjunction of the gametes of Z. diploperennis.The cytological study indicated that there were no univalents and trivalents. Most of the chromosomes paired as bivalents and tetravalents preferently openring. The average of the counts in 214 cells in diakinesis was: 0.24I, 11.29II, 0.06III and 4.20IV. The average of chiasmata was 31.42 and at pachynema some translocations and inversions were observed.In anaphase in the 78% of the cells the same number of chromosomes migrated to each pole and in the left 22% different number of chromosomes migrated towards each pole or remained as lagging chromosomes. Only exceptionally chromatid bridges were observed.The fertility of the pollen is 56% with 80% of fertile seed being the progeny fertile and vigorous.Facultad de Ciencias Agrarias y Forestales