In a decision of November 26, 2013 a Technical Board of Appeal (T 0099/10) has shifted the burden of proof concerning alleged effects of an invention to the patentee. The Board held that if a technical problem set out in a patent is considered to be credibly solved by a claimed invention and if there are no reasons to assume the contrary, it is normally the opponent’s burden to prove that the problem was not successfully solved or at least provide evidence casting doubts on the alleged success of the solution. However, if the opponent succeeds in casting reasonable doubt on the alleged success of the solution, the burden of proof in that respect is shifted to the patent proprietor.