The quantum of induced polygenic variability for quantitative traits was compared in the M₂ and M₃ generations after treating the seeds of Basmati rice cultivar T- 23 with gamma- rays and ethyl methanesulphonate (EMS). There were mutagenic differences for the release of genetic variability in both the generations. In comparison to EMS, gamma-rays were found to be less effective in generating polygenic variation in terms of coefficient of variability. Moreover, the characters differed in the manifestation of variability in the two generations. High induced variability for panicle length, number of grains panicle^-1, plant height, days to flowering and days to maturity was observed in M₂ and for grain yield plant^-1, 100-grain weight and effective tillers plant-1 in the M₃ generation. Therefore, these generations are most appropriate for improvement of these characters through selection.