T 0289/91 (ACE inhibitors) of 10.03.1993

1. The admissibility of the opposition is an indispensable procedural requirement for the substantive examination of the opposition submissions at every stage of the proceedings, i.e. also in appeal proceedings, and, as such, it must be examined by the EPO of its own motion (point 2.1 of the Reasons).

2. A statutory declaration that the opponent is acting on his own behalf may only be required if there are concrete grounds for casting serious doubt on the opponent's true identity. Serious doubts as to the opponent's true identity are not justified by the mere fact that the opponent does not have any obvious personal or economic interest in the subject-matter of the patent (following T 635/88, OJ EPO 1993, 608, point 2.2 of the Reasons).