Over the past two decades, the case law of the Federal Circuit Court of Appeals has made it clear that Section 112 of the patent statute contains two separate requirements relating to the specification of a patent application. It must contain both a "written description" of the invention and an "enabling disclosure." It is possible to meet the latter requirement without meeting the former, for example, when it is clear from the disclosure how one would produce and use a particular thing but the description fails to make any mention of the embodiment in question. Over the past few years, the Federal Circuit Court has used the written description requirement in a number of cases relating to biotechnology so as to limit the scope of claims that can be regarded as being commensurate with the description given. In such cases, some emphasis has been placed by the court on the role of the written description in showing that the inventor was in real life possession of the invention claimed rather than on whether the description contained wording corresponding to the claim language. To this end, earlier decisions in the field of DNA had indicated that an adequate written description of genetic material required a precise definition such as structure, formula, chemical name or physical properties.

The issue came before the Federal Circuit again in Enzo Biochem Inc. v. Gen-Probe Inc. in which the District Court had granted summary judgment of patent invalidity. The broad claim of the patent in suit was to DNA probes which were defined functionally by the ratio of their binding ability to chromosomal DNA of bacteria that cause gonorrhea to their binding to chromosomal DNA of certain other bacteria of the same genus. Other claims related to DNA probes that had been deposited with the American Type Culture Collection (ATCC) and mutants of them. The DNA probes are useful diagnostic tools. The patentees had produced three particular DNA probes falling within their broad definition and deposited them with the ATCC.

Somewhat surprisingly, after an initial decision which held that the patent in suit was invalid for failure to comply with the written description requirement, the court reversed itself following a request for reconsideration by the plaintiff and remanded the case to the district court for further findings of fact as to whether the proper tests for complying with the requirement for a written description had been met.

In its initial decision, the court by a 2-1 majority, after noting that "describing a complicated molecule by means of a broad generic claim (a nucleotide sequence) plus its function fails to distinguish it from other molecules that can perform the same function," went on to conclude that "Enzo claimed anything that works, without defining what works." It had therefore failed to provide a proper written description.

Having reached this conclusion, the majority went on to reconsider whether the purpose of the written description requirement was in fact to show "possession" of the invention or was something else. The issue arose over the question of whether the deposits of DNA that had been made with the ATCC sufficed to meet the written description requirement. The court held that, while the "possession approach" was useful in dealing with questions as to what date a claim might be entitled to, it was irrelevant in situations such as the present where the claim in question was one that had been filed originally. The purpose of the requirement was to enable the skilled person to visualize the invention. Requiring the public to go to a "depository and perform experiments to identify an invention is not consistent with the statutory requirement to describe one's invention in the specification." The possession of three embodiments as was shown by the patentee's deposit of them failed to "provide sufficient distinguishing information about those sequences for the purposes of satisfying Section 112." According to the court, prior case law that had approved the use of a culture collection deposit as a way of meeting statutory requirements had addressed only the question of how to provide an enabling disclosure and not the requirement of a written description of the invention. The majority concluded that, while the use of a deposit was helpful when describing how to make something different from what was deposited, "the deposit here essentially contains the invention, and the invention must be described more than by stating that it exists in a depository."

On reconsideration, the court expressly held that it had been wrong to conclude that the written description requirement could not be satisfied by deposit of biological material with a culture collection when details of that deposit were included in the patent specification. The court noted that the USPTO had expressly formulated rules to permit the use of a deposit as a substitute for a written description when "words alone cannot sufficiently describe how to make and use the invention in a reproducible manner." In view of this, the court decided that such a deposit could be used to satisfy not only the enablement requirement but, in appropriate cases, the written description requirement also. The court then went on to consider whether it was ever possible for a functional definition of a biological material to meet the written description requirement. In doing this, it considered the Patent Office Guidelines on the subject and concluded that this might be possible when the claim included something extra that pointed towards structure, such as a requirement for hybridization to particular DNA. Finally, the court concluded that a determination of whether the deposit of only three biological samples was sufficient to provide a written description for a claim as broad as claim 1, and after noting that the test was whether the actual deposits were representative of the genus claimed, decided that this was a factual matter which needed to be remanded to the district court for a further finding of fact.