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 question by the patent proprietor, no separate communication that the opposition is admissible will be sent to the opponent or the patent proprietor. Where deficiencies on the basis of which the notice of opposition is likely to be regarded as inadmissible, but of which the opponent has not been informed by the formalities officer, come to the attention of the opposition division in the opposition documents submitted to it or because the patent proprietor has raised the issue during the proceedings, it will inform the parties about its reservations in a communication and at the same time request 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 these deficiencies which may no longer be corrected or fails to remedy in good time deficiencies which may be corrected, the opposition division will reject the notice of opposition as inadmissible, possibly after having held oral proceedings. As regards the form of the decision, see E‑X, 2.3 and E‑X, 2.6. For subsequent procedure, see the last two paragraphs of D‑IV, 3.