In particular, the steps in the claimed processes (apart from the natural laws themselves) involve well-understood, routine, conventional activity previously engaged in by researchers in the field. At the same time, upholding the patents would risk disproportionately tying up the use of the underlying natural laws, inhibiting their use in the making of further discoveries.

If a law of nature is not patentable, then neither is a process reciting a law of nature, unless that process has additional features that provide practical assurance that the process is more than a drafting effort designed to monopolize the law of nature itself. A patent, for example, could not simply recite a law of nature and then add the instruction “apply the law.” Einstein, we assume, could not have patented his famous law by claiming a process consisting of simply telling linear accelerator operators to refer to the law to determine how much energy an amount of mass has produced (or vice versa). Nor could Archimedes have secured a patent for his famous principle of flotation by claiming a process consisting of simply telling boat builders to refer to that principle in order to determine whether an object will float.

Patent protection is, after all, a two-edged sword. On the one hand, the promise of exclusive rights provides monetary incentives that lead to creation, invention, and discovery. On the other hand, that very exclusivity can impede the flow of information that might permit, indeed spur, invention, by, for example, raising the price of using the patented ideas once created, requiring potential users to conduct costly and time-consuming searches of existing patents and pending patent applications, and requiring the negotiation of complex licensing arrangements. At the same time, patent law’s general rules must govern inventive activity in many different fields of human endeavor, with the result that the practical effects of rules that reflect a general effort to balance these considerations may differ from one field to another....

In consequence, we must hesitate before departing from established general legal rules lest a new protective rule that seems to suit the needs of one field produce unforeseen results in another. And we must recognize the role of Congress in crafting more finely tailored rules where necessary.

Unfortunately, the justices seemed oblivious to these arguments. And the man who should have been making them, Mayo counsel Stephen Shapiro, completely ignored them. Instead, he seemed to concede the legality of medical patents in general, and focused on nitpicking the details of Prometheus's patent. Specifically, he noted that the patent covers a broad range of metabolite levels and applies for many different autoimmune diseases, and argued that this made the patent invalid.

Asked by Justice Kennedy if a more specific and complex diagnostic technique involving "two or three different drugs" could be eligible for patent protection, Shapiro said yes. "If it leaves room for others to have their own tests with different numbers and different procedures so that it isn't just one test for the whole country, then yes, if it's specific enough," he said. "The specificity is the key."

Justice Scalia pointed out that making patent-eligibility turn on how complex the diagnostic strategy was, or on how many diseases it claimed to address, was totally unworkable. Shapiro's proposal, he said, was "not a patent rule that we could possibly apply."

Justices Scalia and Breyer showed some skepticism that patents could cover the use of scientific correlations in medical practice. But the other justices expressed no such skepticism. At one point, Justice Kagan offered some advice to Prometheus's lawyer. "What you haven't done is say at a certain number you should use a certain treatment, at another number you should use another treatment," she said. "I guess the first question is why didn't you file a patent like that? Because that clearly would have been patentable. Everybody agrees with that."

Prometheus’s patents will also impermissibly restrict public domain activity. These patents’ final step is entirely mental. Patents whose final step is mental have the effect of transforming non-infringing, public domain activity into infringing activity for those who are aware of the thought that triggers infringement. This effect discourages the dissemination of knowledge, because access to patented knowledge places individuals in situations where they must elect to cease doing what was previously a public domain activity—such as reading the results of medical tests—or inadvertently infringe a patent.

For similar reasons, the patents at issue unconstitutionally restrict freedom of thought, by putting parties at risk of incurring damages for patent infringement when they recognize the correlations described in the patents at issue. The First Amendment protects freedom of thought and places limits on patent protections, just as it does on copyright protections. As the Court stated in Eldred v. Ashcroft, 537 U.S. 186 (2003), copyrights could require First Amendment scrutiny if “the traditional contours of copyright protection” were altered. The patents at issue here represent an unprecedented departure from the traditional contours of patent protection; only recently have parties sought patent protection for claims which final element encompasses pure thought. Even if the patents at issue are otherwise patentable subject matter, these patents unconstitutionally restrict freedom of thought in violation of the First Amendment and should be invalidated.

The patents at issue are not “processes” as the term was understood when section 101 of the Patent Act of 1952 was adopted. The Patent Act’s legislative history explains that the term “process” meant “art,” as it had been used in earlier patent statutes. Patentable arts were limited to processes which aimed to produce an effect on matter, and these patents do not.

Moreover, the patents at issue here do not describe a process by either a historic or general definition of the term. A process is a series of actions, and the “indication” element of the claims does not describe an action.

Enforcing the patents here will have a deleterious economic effect on the healthcare and medical research industries and will retard innovation. Empirical evidence shows that other abstract process patents, such as software and business-method patents, have resulted in aggregate financial losses for American firms and have discouraged rather than encouraged innovation. The effect of abstract process patents on software and financial firms will spread to the healthcare and medical research industries if patents such as Prometheus’s are permitted.

"The patents are based on observations of the laws of nature," says David Herbert, chief administrative officer for Mayo Medical Laboratories. "We chose to make a stand." Such "observational" patents increase costs, slow innovation, and worsen patient care, he says. "It doesn't allow the test to be performed close to the bedside, and there's no ability to have second opinions."