The United States Supreme Court recently issued an opinion regarding the patentability of claims directed to diagnostic methods in Mayo Collab. Service v. Prometheus Lab., Inc. In this opinion, the Supreme Court held that correlations between metabolite levels in the human body and either therapeutic efficacy or adverse effects are unpatentable laws of nature. It further found that a patent claim to a method including such a correlation is unpatentable if the remainder of the claim contains only conventional and well-known steps. The Prometheus decision creates uncertainty regarding the scope of patentable subject matter, particularly in the fields of diagnostic and personalized medicine, that will remain until future cases apply this new doctrine.