Background
Mycogen Plant Science owned patents on synthetic insecticidal crystal protein genes — a critical biotechnology involving the Bacillus thuringiensis (Bt) organism — that allow scientists to genetically engineer plants to produce proteins toxic to insect pests. These “Bt patents” covered processes for producing genetically modified plants with built-in pest resistance, which was commercially significant for the agricultural biotechnology industry.
Mycogen sued Monsanto for infringement of the ‘831 patent, which covered processes for making insect-resistant plants. Monsanto had developed similar Bt crop technology using processes during periods when Mycogen’s patents were pending (filed but not yet issued) as well as after issuance. The district court granted summary judgment on several grounds, and both parties appealed. A critical issue was whether Monsanto’s pre-issuance use of the patented process — performed while Mycogen’s patent was still “patent pending” — could constitute infringement under 35 U.S.C. § 271(g).
Section 271(g), added by the Process Patent Amendments Act of 1988, provides that whoever imports into or sells in the United States a product made by a process patented in the United States infringes the patent. The question was whether “patented process” meant a process covered by an issued patent, or whether it could include a process covered by a pending application.
The Court’s Holding
The Federal Circuit affirmed the district court’s ruling that § 271(g) requires the patent to be issued at the time the accused process is performed. “Patent pending” status — however valuable as a business matter — does not confer infringement liability for process patents. The statutory text of § 271(g) refers to products made by a “patented” process, which means a process covered by a patent that has already issued. Products made before the patent issued, even if made by what would later become the patented process, cannot infringe the process patent.
The court also addressed prosecution history estoppel in the context of product claims. Where a patent applicant cancels claims during prosecution, such cancellation creates estoppel in the same manner as a narrowing amendment, preventing the patentee from using the doctrine of equivalents to recapture subject matter surrendered by the cancellation. The court affirmed that estoppel appropriately barred Mycogen’s product claims from being infringed under the doctrine of equivalents.
The Federal Circuit reversed the summary judgment on prior invention, however, finding genuine disputes of material fact about when the competing scientists at different companies conceived and reduced to practice the key inventions — questions that required trial, not summary judgment.
Key Takeaways
- Section 271(g) liability requires the process patent to be issued — not merely pending — when the accused process is performed; pre-issuance commercial use cannot infringe.
- Cancellation of patent claims during prosecution creates prosecution history estoppel that bars doctrine of equivalents arguments, just as narrowing amendments do.
- Questions of prior invention (who invented first, when, and with what diligence) are fact-intensive and typically inappropriate for resolution on summary judgment.
- Biotechnology patent holders cannot retroactively extend § 271(g) protection to cover processes used before their patents issued.
- The case reinforces that the patent grant — not the application — is the source of the enforceable right to exclude others.
Why It Matters
This decision has significant practical implications for the biotechnology and pharmaceutical industries, where companies often invest heavily in developing and deploying processes while competitors’ patents are pending. Mycogen confirmed that early movers who use a process before a patent issues bear no § 271(g) liability — a holding that shaped how companies assessed the risk of using technologies covered by pending applications. Combined with the Patent Pending doctrine, inventors understood that the public notice function of published applications does not create liability; only the issued patent does.
The decision also stands as an important biotechnology patent precedent in the context of Bt crop technology, one of the most commercially significant agricultural innovations of the late 20th century. The ongoing litigation between Mycogen and Monsanto over Bt patents shaped how both companies structured their patent portfolios and licensing arrangements for genetically engineered crops.