SUMMARY- Cuttings of 2x and 4x Ruellia species, their 2x, 3x and 4x hybrids were irradiated at 2, 4 and 6 Krad of gamma rays (Co60). Radiosensitivity of the above penotypes in relation to ploidy and hybridity was studied using the parameters like sprouting of cuttings, survival, growth reduction, final height, number of branches and pollen fertility. Differences in sensitivity of different species of the same ploidy level were noticed. Tetraploids in general, were radioresistant. Hybridity increases the resistance of diploid hybrid above that of its parents. Polyploid hybrids were interme-diate to their parents in radioresistance and the cancellation of the negative andpositive effects of the alleles has been suggested as the probable reason for it. rev (interphase chromosome volume) of all the species and hybrids was determined and the possible correlation of rev with radiosensitivity is discussed.