The comet assay is the method of choice for measuring DNA damage, of various sorts, in human cells such as lymphocytes obtained in the course of population-based studies of environmental and occupational exposure to different genotoxic agents, including radiation, chemicals and oxidative stress. It is noted for its versatility and the breadth of its possible applications. In terms of simplicity, cost, small amount of material required, sensitivity and reliability, the comet assay in its various modifications has few serious competitors. When standardized and validated, the comet assay can provide invaluable information in the areas of hazard identification and risk assessment of environmental and occupational exposure, diseases linked with oxidative stress (e.g. diabetes and cardiovascular disease), nutrition, monitoring the effectiveness of medical treatment and investigating individual variation in response to DNA damage that may reflect genetic or environmental influences. The information obtained could lead to individual advice on lifestyle changes to promote health and especially on relative risks of genotoxic exposure to environmental pollution.