The differences between a cow and a monkey are clear. It is easy to tell a moth from a mosquito. So why are there still scientific studies that mix them up? The answer is simple: hundreds of cell lines stored and used by modern laboratories have been wrongly identified. Some pig cells are labelled as coming from a chicken; cell lines advertised as human have been shown to contain material from hamsters, rats, mice and monkeys.

Which is worse: that such crude mix-ups exist, or that, every day, researchers use cell lines that somebody, somewhere has already found to be mislabelled, misidentified or contaminated? To solve the first problem is a huge challenge. To address the second is a more manageable task, and one that researchers, journals, universities and funders must take seriously.

Nature and the Nature research journals are strengthening their policies to improve the situation. From next month, we will ask authors to check that they are not working on cells known to have been misidentified or cross-contaminated, and will ask them to provide more details about the source and testing of their cell lines.

This may sound like an obvious way to deal with a problem that has been known about for decades. But tests to check the contents of cell lines are complex and time-consuming, and until recently were expensive. What makes the time ripe for action is a combination of a rising awareness of the problem among scientists in certain communities (cancer research in particular), the availability of proper tests and resources (see J. R. Masters Nature 492, 186 (2012), and page 307), and the willingness of some funders to tackle the matter — including the US National Institutes of Health and the Prostate Cancer Foundation in Santa Monica, California.

Problems have already been found with more than 400 cell lines. In the long term, the goal must be to change testing routines worldwide to ensure that new mix-ups are not propagated. The least that scientists should already be doing is checking whether the cell line they are using is one of those already marked with a red flag.

In 2013, Nature journals started to ask authors to report the source of their cell line and whether the cell line had been authenticated. Most have not done so. Out of a sample of around 60 cell-line-based papers published across several Nature journals in the past two years, almost one-quarter did not report the source. Only 10% of authors said that they had authenticated the cell line. This is especially problematic given that almost one-third said that they had obtained the cell lines as a gift from another laboratory.

From 1 May, all authors of papers involving cell lines that are submitted to Nature journals will be asked whether they have checked their cell lines against publicly available lists of those known to be problematic. We will in particular monitor compliance in cancer research. The focus on cancer is a first step, chosen because the cell-line problem has been best documented in this field, and because the cancer community is already reacting to the issue. Some specialist journals, such as the International Journal of Cancer, are now systematically asking for authentication. This is important not only for its effects on basic research, but also because of the potential for translational research to founder if cell lines are contaminated.

Other fields are not immune to cell-line problems, and we hope to extend the systematic checks to them in future. More details of the new policy, whom it affects and where the cell lines should be checked are available at

That a cell line used in a research project appears on a watch-list need not make the research invalid, or mean that the paper will automatically be rejected. Authors will be asked to explain why the misidentification does not undermine the conclusions. But we reserve the right to ask for data to be removed if the justification is judged insufficient by editors and referees.