The admissibility of the opposition must be checked ex officio in every phase of the opposition and ensuing appeal proceedings. It can and, where appropriate, must be raised by the board in appeal proceedings even if this is the first time this matter is addressed (T 289/91, OJ 1994, 649, T 522/94, OJ 1998, 421). On the other hand, as highlighted in T 522/94, the requirement of admissibility must not be circumvented by overemphasising the ex officio principle and shifting the burden of establishing the case from the opponent to the opposition division.