The utility requirement is becoming the most significant hurdle to overcome in seeking patent protection for pharmaceutical and biotechnology inventions.

35 USC § 101 requires that in order to be patentable, an invention must be useful. As noted in connection with the discussion of patentable subject matter, unlike many countries, the United States has always had a broad view of what is useful and the courts have never, for example required that an invention show an advantage over the prior art or be capable of commercialization in order to be patentable. [20]

The leading case is Brenner v. Manson, [21] which had a somewhat unusual fact pattern in that the question before the court was whether an affidavit, submitted in support of an application, showed that the party who filed it had in fact established a utility for the invention in question. The issue before the court related to the production of a compound that had no known utility, although utilities were known for related compounds (the compound in question was a steroid). The majority of the Supreme Court concluded that it did not matter whether an invention was for a product or a process and that in the chemical field unless a claim was for something that was shown to have a specific and substantial utility the metes and bounds of that monopoly are not capable of precise delineation. It may engross a vast, unknown, and perhaps unknowable area. Such a patent may confer power to block off whole areas of scientific development [22] without compensating benefit to the public. The basic quid pro quo contemplated by the Constitution and the Congress for granting a patent monopoly is the benefit derived by the public from an invention with substantial utility. Unless and until a process is refined and developed to this point- where specific benefit exists in currently available form- there is insufficient justification for permitting an applicant to engross what may prove to be a broad field.

The majority of the court concluded with the observation that a patent is not a hunting license. It is not a reward for the search, but compensation for its successful conclusion.

In this decision the court used two words on which little emphasis was placed for the next thirty years but as noted below have become important in the PTO’s approach to biotechnology inventions namely that the utility is both substantial and specific. [23] The next question is how specific must this utility be and what needs to be demonstrated to affirm such utility. The most common situation in which this question arises is in connection with pharmaceuticals, for example in the content of whether demonstration that a compound has an effect in a laboratory animal is sufficient to justify the patentability of that compound. Case law holds that it does at least where the animal tests show some real world utility. [24] In fact case law holds that for any invention a statement of utility in the specification that corresponds to the claims should be taken by the PTO as meeting the requirement of 35 USC 101 unless there is a reason for one skilled in the art to question the objective truth of the statement of utility or its scope. [25]

The position is, however, different where the claim is to a method of treating a disease. In such cases clinical data may in some cases be called for. If the examiner doubts the utility of the invention, as is commonly the situation in cases relating to treatment of difficult-to-cure conditions, one can file an affidavit or declaration proving that the invention does in fact produce the results claimed. [26] Patent Office standards in this area remain strict and claims for treatment of human diseases for which there is no good animal model may require the submission of clinical data. Until recently clinical data was required for almost all claims for treatment of cancer. This standard has now been lowered for some types of cancer where good animal models exist. [27] However, as more knowledge about cancer becomes available and it becomes clear that different types of cancer respond to different treatments, the PTO has become increasingly reluctant to accept claims directed to cancer as such but has required limitation to particular types of cancer. As late as 1995, the PTO still maintained in In re Brana [28] that a showing of efficacy against a cell line used by the National Cancer Institute was insufficient to show utility of chemicals that were stated to be useful "as antitumor substances" and that in vivo data would be needed to make this showing. The Federal Circuit disagreed stating:

For other types of disease, such a treatment of Alzheimer's disease or AIDS, however, clinical data may still be called for, placing a very severe burden on the applicant.