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Blonder Tongue v. University of Illinois

Blonder Tongue v. University of Illinois


In Blonder-Tongue v. University of Illinois from 1971, the court ruled that a plaintiff who loses a civil trial because their patent was ruled invalid cannot continue to bring the same charges against a different defendant even if the defendants are in no way associated. The court made this ruling despite the Triplett v. Lowell case in which the plaintiff continued to name new defendants after losing battles in court.

Case Description

Dwight Isbell from the University of Illinois Foundation created and patented Frequency Independent Unidirectional Antennas. Other entities would go on to create and use similar antennas. In court proceedings, it was ruled that the Foundation's patent on the antennas was invalid because any entity that was familiar with antennas was bound to discover the same antennas as the Foundation, the plaintiff. The plaintiff continued to file claims against defendants despite losing.

Triplett v. Lowell allowed for a plaintiff to name new defendants that were not related to each other. Blonder-Tongue, a defendant, claimed the case should not go to trial because it was already decided that the patent held by the plaintiff was invalid. The defendant believed since there was no patent ownership the case was already decided and more cases on the same topic were a waste of time.


The court ruled to go against the Triplett decision and accept collateral estoppel as a defense. The court agreed that continuing to name defendants in hopes of finally winning a case was a waste of the court’s and defendant’s time. Since the matter had already been adjudged there would be no need to go on with another case, which is referred to as res judicata. If the defendant chose to go on with the court proceedings, that would have been permitted.

All parties are permitted to "have their day in court". If a plaintiff can prove they were not given a fair chance in the first trial to present evidence which led to the losing the case, they may present an argument to go on with a future case regarding the same issue but against a different defendant.

This case put an end to patent ownership trials that have already been decided, yet the plaintiff has decided to keep filing the same hopeless charges against different defendants. United States courts are extremely busy and cannot be subjected to frustrated plaintiffs who continue to name new defendants in patent cases. If a plaintiff has their patent ruled invalid, that decision will carry over to the next case unless they can prove their patent was unjustly ruled invalid.

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