A major project to collect DNA samples and medical data from 500,000 people was launched on Wednesday to study how genes, lifestyle and environment affect the risk of disease.
The UK Biobank, the world's biggest genetic database, will hold millions of samples in a robotically controlled facility near Manchester, England.
The wealth of data that will be collected from men and women volunteers aged 45-69 will help scientists determine the genetic basis of diseases and why some people develop cancer, heart disease, diabetes, asthma or Alzheimer's and others don't.
"Nothing like this has been attempted before in such fine detail on such a vast scale," said Professor Rory Collins, chief executive of the Biobank.
"We will get very reliable information about the causes of disease," he told a news conference.
The $100 million Biobank will be funded by the Wellcome Trust, the world's largest medical research charity, the British government and other sources.
Some researchers have expressed concerns about the design and size of the project, which has been described as the world's biggest medical experiment, but Collins said it has been carefully planned for several years.
Scientists will soon begin collecting blood and urine samples, as well as data on height, weight, body fat and respiratory function from the first volunteers.
Their health will be monitored over future decades to untangle the interaction of how genetics, lifestyle and environmental factors cause disease.
Scientists believe the project could improve prevention, diagnosis and treatment of diseases and help to explain why people react differently to medications.
"Biobank is producing a resource that will be available to scientists from around the world. The scientists will not know about individuals. They will only be able to look at the resource in an anonymous way," said Collins, who is a professor of medicine and epidemiology at the University of Oxford.
Professor Mark Walport, director of the Wellcome Trust, said advances in informatics and the mapping of the human genome in 2000 have made the project possible.
Data from the Biobank, which will contain about 10 million biological samples, will be available to scientists who can submit an application to use it for their research.
Professor Nigel Mathers, of the Royal College of General Practitioners, described Biobank as one of the most important scientific endeavors of the 21st century.
"It will build on our existing knowledge of epidemiology and initiatives such as the Human Genome Project to create a database of information and samples," he said in a statement.