Japan's drive to regulate experimental stem-cell treatments is a welcome step (Nature 494, 5; 2013). However, it could be hard to define universally applicable criteria that ensure the safety and effectiveness of such treatments worldwide.

There is a risk that the social and economic circumstances of patients and researchers might blur or compromise crucial criteria, such as evidence-based support (including adequate preclinical and clinical testing), ethical review and no-fee experimental treatment.

Stem-cell therapies are all too often unsupported by scientific evidence, but many patients are prepared to accept the risks. And nations with inadequate health-care resources may expect patients to pay for experimental treatments.

Proliferation of experimental stem-cell therapies may even be indirectly encouraged in countries such as China, where ultra-light regulation through official notification (see www.moh.gov.cn) has uncertain regulatory value.