The public has become more aware that exposure of males to certain agents can adversely affect their offspring. The hazards associated with exposure to ionizing radiation have been recognised for nearly a century. There was a civil court case on behalf of two of the alleged victims of paternal irradiation at Seascale against British Nuclear Fuels. The case foundered on “the balance of probabilities”. Nevertheless, there was support for paternal exposure from Japanese experimental X-ray studies in mice. The tumours were clearly heritable as shown by F2 transmission in vivo. In addition in humans, smoking fathers appear to give rise to tumours in the F₁ generation. Using rodent models, developmental abnormalities/congenital malformations and tumours can be studied after exposure of males in an extended dominant lethal assay and congenital malformations can be determined which have similar manifestations in humans. The foetuses can also be investigated for skeletal malformations and litters can be allowed to develop to adulthood when tumours, if present, can be observed. Karyotype analysis can be performed on foetuses and adult offspring to determine if induced genetic damage can be transmitted. Using this study design, cyclophosphamide, 1,3-butadiene and urethane have been examined and each compound produced positive responses: cyclophosphamide in all endpoints examined, 1,3-butadiene in some and urethane only produced liver tumours in F₁ male offspring. Using reactive oxygen species which are known to be produced during ionizing radiation, we examined human sperm and lymphocytes in vitro after treatment with six oestrogenic compounds in the Comet assay, which measures DNA damage, and observed that all caused damage in both cell types. The damage was diminished in nearly all cases by catalase, and in some instances by superoxide dismutase (SOD) and Vitamin C (Vit C). This response pattern was also seen with hydrogen peroxide. This similarity suggests that the oestrogen-mediated effects could be acting via the production of hydrogen peroxide since catalase always markedly reduced the response.