On 6 and 9 August 1945, nuclear bombs dropped by the United States flattened the Japanese cities of Hiroshima and Nagasaki. The explosions killed 120,000 people; at least twice as many have since died from the effects of being exposed to radiation.

The attacks changed the political landscape for ever, but they have also made a major impact on science. The Radiation Effects Research Foundation (RERF) laboratories in Hiroshima and Nagasaki have tracked more than 80,000 survivors of the bombings, and the knowledge gained now forms the basis of our understanding of how radiation causes cancer, as well as the radiation protection standards used in hospitals and nuclear facilities. Yet 60 years on, uncertainties over US funding, and the foundation's ageing facilities, are causing fears about the future of a project that is still far from the end of its scientific life.

Over the past six decades, researchers at RERF have collected vast amounts of data from surveys, health examinations and biological samples, providing a resource for epidemiologists around the world. The survivors were a normal slice of the Japanese population. And unlike subsequent disasters such as Chernobyl, where some of the exposure came later through environmental contamination, almost all the radiation was delivered when the bomb detonated, making it easier to estimate each person's dose.

“We are talking about the biggest epidemiological study ever conducted,” says Yuri Dubrova, an expert on the effects of radiation on the human germline at the University of Leicester, UK. “The data from RERF produced information that is still the gold standard in terms of cancer studies. This is ongoing and astoundingly important research.”

Charles Land of the US National Cancer Institute in Bethesda, Maryland, says that with some 45% of survivors still alive, the most useful information may be yet to come. “There's still a lot to learn,” he says. “As the exposed population ages, there is going to be a lot more information coming from the survivors.”

Studies over the past decade or so are also starting to suggest that exposure to radiation increases the risk of many diseases besides cancer, and that there may be no safe dose for treatments such as radiotherapy (see ‘Fallout beyond cancer’).

But despite the project's value, many experts are worried about its future. The foundation's budget has been around ¥3.8 billion (US$33.8 million) for several years. Until 1996, half of that came from the United States, but its contribution has dropped to 38%.

Then last year, the US Department of Energy (DoE) suggested cutting its annual contribution. Full funding was eventually delivered four months late and is guaranteed for another two years, but some are edgy that a similar situation could arise again. “Let's hope the DoE doesn't try any more of the tricks it did last year,” says Mark Little, an epidemiologist at Imperial College London. “It's vital they keep going for the foreseeable future.”

Out of the ashes: survivors of Hiroshima and Nagasaki form ‘the biggest epidemiological study ever’. Credit: HULTON ARCHIVE/GETTY IMAGES

Little has worked with data from RERF for the past 15 years, and was lead author of a letter sent to The Lancet last year in protest at the proposed budget cuts (M. P. Little et al. Lancet 364, 557–558; 2004). He says that the foundation's facilities in Hiroshima, housed in prefabricated huts built in 1949, are run down. Roofs leak and leaves blow into labs. There are also staffing problems. “There have been significant departures of epidemiologists,” says Little. “They are struggling to do the analysis on the latest samples.”

Dale Preston, an epidemiologist formerly at RERF, shares Little's concerns. “Over the past few years people have been less keen to work in this area,” he says. “But there's nothing that can do the kind of work RERF can do.”

Kazunori Kodama, chief scientist at RERF, says that work is continuing for the time being. “The place is holding out right now,” he says. “But I'm still worried about what will happen after 2007.”

Additional reporting by Jim Giles in London, and Ichiko Fuyuno and David Cyranoski in Tokyo