5.1 Inadmissibility at a later stage 

The admissibility of the opposition must be examined ex officio in every phase of the proceedings. In particular, the opposition division examines whether the notice of opposition is adequately substantiated (see D‑IV, 1.2.2.1(v)).

Since the admissibility of an opposition is always open to challenge from the patent proprietor, no separate communication that the opposition is admissible will be sent to the opponent or the patent proprietor. Where deficiencies likely to render the opposition inadmissible but not brought to the attention of the opponent by the formalities officer are discovered by the opposition division either in the opposition documents submitted or when the patent proprietor points to them during the proceedings, the opposition division will inform the parties about its reservations in a communication and at the same time invite the opponent in question to submit observations. If deficiencies within the meaning of Rule 77(2) are involved, it is sufficient to specify a period for the opponent to remedy such deficiencies.

If the opponent does not successfully refute the opinion expressed by the opposition division on the existence of deficiencies that may no longer be corrected or fails to remedy in good time deficiencies that may be corrected, the opposition division will reject the opposition as inadmissible, possibly after having held oral proceedings. As regards the form of the decision, see E‑IX, 2.3 and E-IX, 2.6see E‑X, 2.3 and E-X, 2.6. For subsequent procedure, see the last two paragraphs of D‑IV, 3.