Questions about the effects of patents and licensing are becoming critical in the United States, Europe and other developed countries as more genes are discovered and patented, and as genetic testing becomes an integral part of standard medical care. The award of patents for the diagnostic test for haemochromatosis, a progressive iron-overload disease, joins an ever-growing list of such tests that have been, or will very soon be, patented. We have found that US laboratories have refrained from offering clinical-testing services for haemochromatosis because of the patents. A lot of clinical study is needed to validate and extend the early discovery of a disease gene such as that for haemochromatosis, so our results give us reason to fear that limiting clinical testing will inhibit further discovery as well as the understanding that emerges naturally from broad medical adoption1. As highlighted by the looming patent battle over testing for a breast-cancer mutation between Myriad Genetics and the French Curie and Gustave Roussy institutes (see ref. 2), restrictive licensing and monopolization of clinical-testing services will not be limited to the United States for long. Indeed, four patents relating to haemochromatosis testing are pending in the European Patent Office, suggesting that the situation in the United States described here may soon spread to Europe.