SynopsisStudies on sorghum seed irradiated with X-rays and thermal neutrons produced the following general results: The height of seedlings from irradiated seed was reduced with increases in dosage. Plants grown from irradiated seed exhibited depressed stature. All radiation dosages delayed the anthesis and shortened the blooming period. The average sterility ranged from 12.5 to 75.8% in the lowest and the highest radiation doses, respectively. The corresponding averages of number of bridges per cell were 0.2 and 1.53 and frequencies of seedling mutants 2.7 and 7.3%. Estimates for biological equivalence of thermal neutrons to 1 r of X radiation were obtained.