After 40 years of studies on the children of atomic bomb survivors and a suitable control population in which no statistically significant genetic effects of A-bomb radiation were observed, two new projects have been initiated in order to detect mutations in the DNA and RNA molecules. Permanent cell lines from peripheral B-lymphocytes from approximately 500 families composed of exposed parents and their children and approximately 500 control families are being established by Epstein-Barr virus transformation. Cells will be sources for DNA and RNA samples in the screening for mutations. After comparison of efficiencies of the scanning techniques, we selected the denaturing gradient gel electrophoresis (DGGE) of DNA fragments amplified by polymerase chain reaction (PCR) for our purpose. A small scale pilot study has started to solve problems and obtain a better efficiency in this approach. Current thinking about the most efficient procedures is presented.