Drosophila melanogaster adults are irradiated and then mated to flies containing genetic markers and/or crossover suppressors in all chromosomes. Appropriate genetic schemes are followed to obtain balanced stocks of entire treated genomes. Each chromosome of each genome is observed for visibles, lethals, detrimentals and sterility factors. Tests are made for translocations involving any combination of chromosomes. All chromosomes of each genome are examined cytologically for possible deficiencies, inversions, transpositions, etc. and to determine the break points of the translocations. It is believed that a study such as this will give us a far better idea of the overall magnitude of radiation-induced genetic damage and a better insight into the nature of this damage, expecially the inter­-relationships between the different kinds of genetic alterations, than has heretofore been possible with studies of selected types of damage in selected chromosomes or loci.