Once again, Seoul National University's Woo Suk Hwang is this week being accused of possible impropriety in allegedly obtaining human eggs for the first experiment to derive human stem cells from a cloned human embryo.

His accuser this time is Gerald Schatten of the University of Pittsburgh, a long-time collaborator of Hwang's. In a statement on 12 November announcing that the collaboration will now end, Schatten cites charges, first aired in Nature in May last year, of “oocyte donation irregularities” at Hwang's laboratory (see Nature 429, 3; 2004).

There were calls for an investigation back then, but South Korea's handful of bioethicists had no leverage, and nothing happened (see Nature 429, 490; 200410.1038/429490b). Much of the Korean media repeated and endorsed Hwang's denials. Far from launching an investigation, the government backed his research with generous funding and dedicated a postage stamp to him. Some politicians even pledged to spearhead a drive to win him a Nobel prize.

Stem-cell researchers worldwide were scarcely more critical, perhaps fearing that any suggestion that this high-profile research had rested on an unethical practice would stain a field that has enough controversy attached to it already. As the situation in Japan amply demonstrates, such fears can rapidly thwart research opportunities in this sphere (see page 262 of this issue).

Schatten's actions reopen the questions raised last year. Did the experiment use eggs donated by a graduate student or by a member of the research team? Did donors receive payment for their eggs? Hwang has vigorously denied these allegations.

But this time, it will be harder for the Korean authorities to ignore these questions. The Korean media is taking a more critical view. According to some reports, Ky Young Park, the president's adviser for science and technology, has already promised an investigation.

To maintain public support, researchers need to follow strict ethical guidelines — and be seen to be doing so.

An investigation led by Park would be less than optimal, however, as she was a co-author on the Hwang paper (Science 303, 1669–1674; 2004). She subsequently described her role in the work as that of a ‘bioethics consultant’ — and told Nature that she hadn't given any thought to the ethics of egg donation.

Park's real role in the work remains something of a mystery. Almost anyone else would be better placed to investigate this episode, but it remains to be seen who will do it. The ministry of science and technology does not seem to be keen. As time passes, an inquiry may become more difficult to conduct.

A thorough investigation is nonetheless required, not just for the sake of scientific integrity in South Korea, but to help persuade sceptics worldwide that research on human embryonic stem cells is being done ethically. This field of research could yet prove to be immensely fruitful, but it requires strong public support.

Stem-cell researchers will now find themselves on the defensive in proving that they are ready to stick to strict ethical codes. Just when Hwang was tying together an international stem-cell network with his laboratory at its hub (Nature 437, 1077; 2005), these allegations will reverberate around the world of developmental biology.

To maintain public support for any controversial field of science, researchers need to follow strict ethical guidelines — and be seen to be doing so. If for whatever reason that doesn't happen, responsibility jumps up a level. It then becomes the job of regulatory bodies and funding agencies to ensure that researchers are brought to account. Is anyone in South Korea going to step up to the task?