Invocation of attorney-client and/or work product privilege by infringement defendant does not give rise to adverse inference with respect to willful infringement, since there should be no risk of liability in disclosures to and from counsel in patent matters; nor does defendant’s failure to obtain legal advice give rise to adverse inference, in view of burdens and costs of requirement for early and full study of every potentially adverse patent of which defendant had knowledge. The court answered the following four questions: (1) When the attorney-client and/or product privilege is invoked by a defendant in an infringement suit, is it appropriate for the trier of fact to draw an adverse inference with respect to willful infringement? The answer is “no.” (2) When the defendant had not obtained legal advice, is it appropriate to draw an adverse inference with respect to willful infringement? The answer is again “no.” (3) If the court concludes that the law should be changed and the adverse inference withdrawn as applied to this case, what other consequences are there for this case? The court held that adverse inferences of unfair rule opinions cannot be drawn. (4) Should the existence of a substantial defense to infringement be sufficient to defeat liability for willful infringement even if no legal advice has been secured? The answer is “no.” Precedent includes this factor with others to be among the totality of circumstances, stressing the “theme of whether a prudent person would have sound reason to believe that the patent was not infringed or was invalid or unenforceable, and would have so held if litigated.” (Knorr-Bremse Systeme Fuer Nutzfahrzeuge GmbH v. Dana Corp., 72 USPQ2d 1560, CA FC, 9/13/04).