THE PROMISE of the Human Genome Project - to identify and treat the genetic causes of disease - has not been achieved. How genes affect cells and cause or prevent disease is not as simple as switching individual genes on or off. In the last decade, our understanding of the complex inter retionships of genes and the impact on them of environmental conditions has grown. We can say with increasing confidence that exposure to stressors (physical, nutritional and emotional), before conception, prenatally and throughout Life, has a measurable effect on genetic expression. Nurses need to be aware of current research and theories in genetics. Counselling women during their reproductive years about how nutrition and lifestyle will affect the health of their unborn children is a useful nursing role. Genotyping of individuals is becoming popular, and genetic engineering techniques more accessible. We need to understand what these can, and cannot, provide in terms of health risks and disease management. Understanding new technologies related to genetics and epigenetics can allow nurses to share fully in the discussions about ethical and safety concerns.