In a breeding programme aimed at developing tetraploids from Australian adapted germplasm, a root-tip squash technique was initially used for ploidy determination. The highest recovery of tetraploids (39.7%) was obtained by treatment of 1-week-old seedlings with 0.1% colchicine concentration. Significant cultivar × colchicine concentration interaction was observed in seedling survival, highlighting the difference in response of the cultivars to colchicine treatment. Subsequently, flow cytometric estimation of the nuclear DNA content in young leaf tissues was used to screen the C 1 and C 2 generations. The speed and the efficiency of this method make it possible to examine a large number of plants. In the C 1 population the percentage of tetraploids, diploids, and aneuploids was 25, 72.7, and 2.3% respectively, while in the C 2 generation the percentage of tetraploids, diploids, and aneuploids was 43, 2, and 55% respectively.