Any amendments made in opposition proceedings must be occasioned by the grounds for opposition specified in Art. 100. That is to say, amendments are admissible only if they are required in order to meet a ground for opposition. However, the ground for opposition does not actually have to have been invoked by the opponent. For example, in opposition proceedings admissibly opened on grounds of non-patentability, the patent proprietor can also submit amendments to remove added subject-matter. Opposition proceedings cannot be used merely to tidy up and improve the disclosure in the patent specification (see T 127/85, OJ 7/1989, 271). The mere addition of new claims to the claims as granted is inadmissible because such amendments cannot be said to meet a ground of opposition. However, the replacement of one independent claim as granted by multiple, e.g. two, independent claims each directed to a respective specific embodiment covered by the independent claim as granted is admissible if such a replacement is occasioned by grounds of opposition specified in Art. 100 (T 223/97, not published). Apart from the above, amendments occasioned by national rights of earlier date are admissible pursuant to Rule 87 (see also C-IV, 6a, with the exception of withdrawing the designation, and the reference in VII, 4.5, to C-III, 8.4).

If the proprietor proposes amendments to the patent in reply to the grounds of opposition and the Opposition Division intends to maintain the patent in amended form, pursuant to those grounds, other amendments, not related to the grounds of opposition (e.g. corrections, clarifications), may be allowed provided that the patent thus amended still fulfils the requirements of the EPC. Such amendments, however, should not be proposed by the Opposition Division and they can only be taken into consideration up to the pronouncement of the decision (in oral proceedings) or until the date the decision is handed over to the EPO's internal postal service for transmittal to the parties (in written proceedings) (see G 12/91, OJ 5/1994, 285).

The amended documents should, provided that it is not irrelevant at the stage reached in the procedure, be as complete as possible and drawn up in such a way as to allow the European patent, where appropriate, to be maintained without further delay in the amended version.

These considerations apply also to documents of second preference in which the proprietor proposes amendments for consideration by the Opposition Division only if the Division is unable to grant his main request, for example that the opposition should be rejected. In both cases, however, it will be more convenient in certain circumstances to determine first the form of the claims, leaving purely consequential amendments in the description to be dealt with later.

Care must be taken to ensure that any amendments do not offend against Art. 123(2) and (3) (see V, 5 and 6). The proprietor of the patent should, where this is not obvious, indicate the points in the original application documents or claims of the granted patent from which the amendments may be derived (Art. 100(c) and Art. 123(2)). In addition, he should file observations as regards the patentability of the subject-matter of the patent as amended (with reference to Art. 100(a) and 100(b)), taking into account the state of the art and objections raised in the opposition notice together, where appropriate, with the evidence presented in support. It must also be checked that the patent, by the amendments themselves, does not contravene the requirements of the EPC (with the exception of Art. 82, see V, 2). For the form of amended documents, see E-II.