This is a collaborative study with the Ukrainian National Research Center for Radiation Medicine (URCRM) of trios of parents and their offspring. Data for about 450 pairs of parents with preconceptional doses and their offspring would be collected. At least one of the parents of each pair would have been exposed to radiation from the Chernobyl accident, either as clean-up worker or as evacuee. The plan is to investigate purely preconceptional effects and also the effects of in utero exposure. It is hoped that more children (siblings of the existing offspring) could be added to these trio families, some of whom are quite young. Preliminary dosimetry exists for some trios, implying that radiation doses (to the parental gonads) span a wide range, from 0 to over 3 Gy. This will be expanded, using personal information on the conditions of exposure (residential history, dietary habits, countermeasures applied, etc.), obtained by interview.