Warner-Jenkinson v. Hilton Davis (JWB)

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The Case

  • 1985 ‘746 patent for Hilton Davis issued, disclosing improved purification process involving the “ultrafiltration” of dye through a porous membrane at pH levels between 6.0 and 9.0 (clarified pH because of “Booth” patent)
  • 1986 Warner-Jenkins (petitioner) created own ultrafiltration process, at pH levels of 5.0
  • Respondents sued for infringement based on doctrine of equivalents
  • Federal Circuit affirmed District Court ruling, holding that the doctrine of equivalents continues to exist, that the question of equivalence is for the jury to decide, and that the jury had substantial evidence from which to conclude that petitioner's process was not substantially different from the process disclosed in the '746 patent

The Patent

  • membrane having nominal pore diameter of 5-15 Angstroms under a hydrostatic pressure of 200-400 psi, at a pH of 6.0 to 9.0
  • alleged infringer: 5-15 Angstroms, at pressures of 200 to nearly 500 psi., and at a pH of 5.0

Doctrine of Equivalence

  • Petitioner argued doctrine of equivalents is inconsistent with 1952 Patent Act
  • Court feared that the doctrine conflicts with numerous holdings that a patent may not be enlarged beyond the scope of its claims. Way to reconcile is to apply doctrine to each of the individual elements of a claim, rather than to the accused product/process as a whole.
  • “Prosecution history estoppel” – a surrender of matter during patent prosecution limits the recapturing of that subject matter, even if it is equivalent to the matter claimed
    • This does not bar all equivalents from being claimed
  • Graver Tank does not require proof of intent of infringer before applying doctrine of equivalence
  • Warner-Jenkinson argued that doctrine of equivalence must be found by Court, not by jury
    • Jury found ‘746 patent valid and infringed by DoE, but that Warner-Jenkinson did not intentionally infringe, so only awarded 20 % of the sought damages
    • Jury also forbade Warner-Jenkinson from practicing ultrafiltration below 500 psi and below 9.01 pH
    • Court of Appeals affirmed


  • equivalency must be determined against the context of the patent, the prior art, and the particular circumstances of the case (no formula)
  • Each element contained in a patent claim is deemed material to defining the scope of the patented invention, and thus the doctrine of equivalents must be applied to individual elements of the claim, not to the invention as a whole
  • According to petitioner, any surrender of subject matter during patent prosecution, regardless of the reason for such surrender, precludes recapturing any part of that subject matter, even if it is equivalent to the matter expressly claimed
    • There was no reason for the inclusion of the 6.0 pH lower limit – it is not precluded by prosecution history estoppels
    • if it was added to avoid conflicting Booth patent, that’s a different story (for the Federal Court to decide, on remand)
  • Just because Graver Tank references copying and piracy does not limit its application to only those cases
  • Graver Tank does not require intent-based elements in the doctrine of equivalents
  • The determination of equivalence should be applied as an objective inquiry on an element-by-element basis.
  • Prosecution history estoppel continues to be available as a defense to infringement, but if the patent holder demonstrates that an amendment required during prosecution had a purpose unrelated to patentability, a court must consider that purpose in order to decide whether an estoppel is precluded.
  • Remanded to find what purpose of 6.0 lower limit was, and if it was for patentability, equivalence cannot be found

Class Notes

  • Hilton Davis’ process ranged from pH levels of 6.0 to 9.0
  • Warner-Jenkins’ alleged infringing process worked at pH levels of 5.0
  • Argument in lower courts is that pH = 5 is equivalent to pH = 6
    • 5 is ten times more acidic than 6 (pH is logarithmic scale)
  • Upper end (9.0) was to avoid infringement of prior art, but lower end (6.0) has no clear reason
    • on remand, patentee will have burden of proving why lower end was established

Petitioner: Doctrine of Equivalence

  • Statutory burden on patentee to draft his/her claims
  • Allows for reissues (to fix mistakes)
  • Means-plus-function claims gave them more scope so the doctrine is no longer needed


  • 1952 Patent Act is not different than 1870 Act (Doctrine of Equivalence is nothing new)
  • en banc = tried before a whole bench of judges instead of just a panel (12-15 judges rather than 3)
  • way to fix: instead of considering each patent as a whole, consider element by element within each claim
    • decrease ambiguity
    • avoid being unbounded – but is it really unbounded?

Doctrine of Equivalence

  • There are limitations of claims, some for patentability, some for no reason at all
  • In doctrine of equivalence, if limitations were put up to avoid prior art, you cannot go past that limit for equivalence
  • Because 6.0 was not clear, it was remanded