Under the United States Food and Drug Administration's Expanded Access program, a physician may treat a single patient with an experimental medication under an individual investigational new drug application (iIND). Metabolic geneticists may be among the specialists most likely to be asked to obtain an iIND, because there are many experimental treatments for inborn errors ofmetabolismwhich work in animals but suffer delays in translation to the bedside. The iIND has the potential to help bridge that gap, by gathering initial evidence in support of the use of an experimental drug in humans. If donewith experimental rigor, the datawill be useful, despite being limited to a single patient. However, iINDsmay pose risks to drug development if patients are not carefully selected. Whatever their advantages and disadvantages, iIND studies are here to stay. Metabolic specialists should cautiously consider the iIND as a tremendous opportunity for therapeutic experimentation.