1. Some preliminary experiments are described with C2- and C3-generations of tetraploid Italian ryegrass. In all cases the tetraploids had a lower dry matter content than the diploids. 2. A C3-generation produced by mass selection equalled or surpassed the diploid mother strains in dry matter yield in some small experiments on several soil types in the first year. The tetraploids, however, were less leafy and showed reduced stands in the second year, even after a mild winter. 3. By maternal line selection C2- and C3-families were obtained which were more rapid in initial development and in spring growth, more winterhardy, more leafy and more resistant to fungus attack and to bad weather conditions than the diploid strains. Several families and a synthetic, based on some of them, produced more dry matter, both in the first and in the second year. 4. Families selected on the basis of fertility and forage yield produced in a small experiment more spikelets per ear, more seeds per spikelet, a higher thousand kernel weight and a higher seed yield per m2 than the corresponding values recorded for diploid strains. 5. From the data available it is concluded that chromosome doubling offers favourable possibilities for the improvement of Italian ryegrass.