The deep pockets of many US institutions, and a select few in the UK, attest to the high cost of attaining success in the sciences. Where are the world's top scientists? Over the four years of The Times Higher-QS World University Rankings, the verdict of the experts we poll has been unanimous: the world's top scientists are in the UK and the US. Last year, they made Cambridge and Oxford the top two science universities. This year, they have chosen the University of California, Berkeley, and the Massachusetts Institute of Technology, with Cambridge and Oxford in third and eighth places respectively.

In this table and the following faculty-specific rankings, we place universities in order of the opinions of our peer reviewers, who are active academics in the subjects on which they are giving their views. This year they have put US and UK universities in the top 11 places. Tokyo, in 12th position, is the top institution from any other country.

But there is no room for British triumphalism. The large amount of research funding that goes into a small number of UK universities appears, on the evidence of this table, to buy top performance for a few universities, but is less good at building strength in depth. The US has 24 universities in this top 50, but the UK manages only three, putting it level with France and Canada, behind Australia.

France and Germany's relatively modest showing in this table is often attributed to the fact that many of their scientists work in state labs, not universities. This argument is strengthened by this year's Nobel prize awards. The prize for physics was shared by Albert Fert, who works partly for the company Thales and partly at Universite Paris-Sud, and Peter Grunberg, who works in the Julich research centre in Germany. The prize for chemistry went to Gerhard Erlt, who is based at the Max-Planck Society, the biggest German research institution. However, we are ranking universities, not countries.

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This table also shows citations per paper over a five-year period for science publications, as measured by Scopus. Because the subject area being analysed is similar for each institution, this shows which universities are producing research with the most impact. We have not aggregated the two columns to produce an overall score. Experts on composite tables such as this agree that combining just two measures such as these would not produce a meaningful result.

Some US institutions such as New York University are rated far more modestly by other researchers than their citations might suggest. At the other extreme, 11 of the top 20 universities as measured by our peer reviewers manage fewer than seven citations per paper.

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Drew Faust, installed last month as president of Harvard University, can draw comfort from the fact that her university is number one in the world overall, as well as in life sciences and biomedicine, with its biggest component, Harvard Medical School, regarded as the best. And so it should be. It has more than 11,000 staff, an annual budget of $470 million (?230 million) and an endowment given as $3,256,509,589.

Not everyone agrees that Harvard is top of the medical tree. It has won only two Nobel prizes for medicine since 1981. But the esteem in which it is held by biomedical academics around the world suggests it is producing key discoveries at an impressive rate.

There may be arguments about where the best economists or historians ply their trade. But this table shows that the sheer amount of cash available for medical research in the US enables it to dominate this high-pressure, big-money field, with 22 of the top 50 institutions. The funds open to US institutions include about $23 billion a year for universities from the National Institutes of Health, plus funding from large medical charities and a range of government bodies such as the Veterans Health Administration. The Bill and Melinda Gates Foundation adds further to US resources for biomedical research.

However, this table suggests that recent increases in UK health research are paying off. The field is led by the Medical Research Council, whose budgets have grown rapidly in recent years and are set to expand further as its activities are co-ordinated more closely with National Health Service research. And as well as state funding via the MRC, the UK is home to the Wellcome Trust, the biggest medical charity outside the US. Cambridge and Oxford appear second and third, with Imperial College London seventh. A total of seven UK universities are in this top 50.

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We separate this analysis from our look at the rest of the sciences because the sheer amount of biomedical research, and its ferocious publishing culture, would swamp the less prosperous and cut-throat natural sciences if we merged the two. But as well as being important and well- funded, biomedical research is controversial: think of stem cells or xenotransplantation.

But there is little here to suggest that the Bush Administration's unease about some of these developments is hobbling medical scientists in the US. Apart from some high-profile defections to Asia and Europe, the US is where the top researchers in this field want to be.

Asian nations with ambitions on the world stage have realised that biomedicine offers a unique chance to carve out new industries and markets. Universities in Singapore, Korea, Hong Kong and China appear in this table along with more established institutions in Japan, Australia and New Zealand. Our citations data suggest they are producing some well- regarded papers.

By contrast, Chinese and Russian universities are well liked by their academic peers but produce few high-impact research papers.

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