Under Art. 111(2) EPC the EPO department of first instance whose decision was appealed is bound by the ratio decidendi of the board of appeal if the case is remitted to it.

The board in T 366/92 pointed out that according to Art. 111(2) EPC 1973 the examining division was bound by the board's decision only to the extent that it had been decided that the subject-matter of Claim 1 was novel when compared with the prior art known from D2 and that the claim met the requirements of Art. 84 and 123(2) EPC 1973. See also T 255/92.

When after remittal the proprietor files new requests which require examination to be re-opened on issues that have already been judged upon by the board of appeal, without the justification that might be provided, for example, by the proprietor's being faced with a new situation, then such requests should be deemed inadmissible (T 383/11).

In T 308/14 the board held that if a case is remitted to the opposition division in appeal proceedings, after the board has taken a decision under Art. 84 EPC on the clarity of a certain feature in a claim, this decision is res judicata and thus binding on the opposition division in the subsequently resumed opposition proceedings. The binding effect did not only cover the decision on Art. 84 EPC as such; it also extended to any finding of fact that led to this decision. Therefore, if in the resumed opposition proceedings an insufficiency objection is made under Art. 83 EPC on the basis that this very feature was ambiguous (insufficiency arising out of ambiguity), the opposition division should not reopen the discussion on whether this feature is clear, and should accept any finding of fact that the board made in arriving at its decision on Art. 84 EPC.

According to T 934/91 (OJ 1994, 184), a board's decision apportioning costs constituted an absolute bar to the opposition division's considering afresh, let alone deciding upon, either the fact or the quantum of the apportionment, or their reviewing the reasons (ratio decidendi) for which the apportionment had been made. The board found that the purported decision of the opposition division on this point was in law a mere communication of the clear and immutable legal position brought about by the earlier decision of a final court of competent jurisdiction, namely, the technical board of appeal.

However, a board of appeal decision has the binding effect referred to in Art. 111(2) EPC only if the case is remitted to the department of first instance. A board of appeal decision in another case is not binding on the department of first instance (see T 288/92; and also J 27/94, OJ 1995, 831).