On March 4, 2014, the United States Patent and Trademark Office (USPTO) issued final guidance to the Examining Corps regarding patent eligibility of claims involving laws of nature, natural phenomena and natural products. The 18 page memorandum, entitled “Guidance For Determining Subject Matter Eligibility Of Claims” (the “Guidelines”), interprets and extends the Supreme Court’s holdings in Association for Mayo Collaborative Services v. Prometheus Laboratories, Inc. (Prometheus) and Molecular Pathology v. Myriad Genetics, Inc. (Myriad). The Guidelines provide an analytical rubric and detailed examples that Examiners will use to assess whether claims involving laws of nature/natural principles, natural phenomena, and/or natural products are patent eligible subject matter. Notably, the Guidelines extend the holding of Myriad beyond isolated nucleic acids and instruct Examiners that isolated natural products are not patentable subject matter. While these Guidelines are not legally binding and the courts will ultimately interpret Prometheus and Myriad and clarify what subject matter is patent eligible, the Guidelines will at this time significantly impact the scope of claims relating to laws of nature and natural products the USPTO is willing to grant. In this client alert, we will briefly review the Prometheus and Myriad holdings, provide a summary of the Guidelines, and finally offer some forward looking considerations flowing from these new examination criteria.