In the first phase of the Human Genome Project, new and ingenious tools have made it possible to map all the individual nucleotides that make up the 23 human chromosomes. During the next 5 years, the 3 billion DNA bases and the 50 000 to 100 000 genes will be sequenced. This knowledge will have widespread applications in biology, medicine and industry. The genetic research community currently has access to abundant DNA markers, detailed chromosome maps, extensive online databases as well as rapid DNA analysis technologies, all of which can be used to identify disease-causing genetic mutations. In the next 15 to 20 years, the Human Genome Project is expected to identify defective genes causing thousands of hereditary diseases, including common diseases such as heart disease, diabetes, asthma and cancer. The hope is that these discoveries will lead to better understanding of the causes of these diseases, and to better approaches to diagnosis, prevention and treatment of human genetic disorders.