Dormant seeds of two partially asynaptic strains, K-642 and K-648, in which 2 to 8 univalents were present at the first metaphase of meiosis, and a normal cultivar Kinmaze were irradiated with gamma rays of 0 to 30kR. The survival rate at maturity of the X₁ plant was reduced to a marked extent in K-642 and K-648 compared with Kinmaze. The mean seed setting in K-648 was slightly less than in Kinmaze. The incidence of chlorophyll mutations in Kinmaze increased linearly with the radiation dose. In contrast, the mutation frequency in K-648 was found to increase more rapidly than a single power of the dose of gamma rays. Supposing that the loose association of homologous chromosomes in somatic cell is correspondent with the failure of hromosome pairing at meiosis, the results obtained in this experiment provide the evidence of a common basis for repair and recombination mechanisms even in rice.