In T 142/97 the board held that the opposition division had violated the opponent's right to be heard under Art. 113(1) EPC 1973 by not hearing the witness offered in connection with a prior use that had been adequately substantiated in the notice of opposition.
In T 269/00 the board held that the case before it differed from T 142/97 because the ground of prior use was not adequately substantiated during the opposition period, but completed piecemeal during the opposition proceedings. The board concluded in the case at issue that not calling to oral proceedings a witness who had been offered by one party to confirm a fact did not amount to a substantial procedural violation.
In T 959/00 the opposition division had not replied to the opponent's offer to hear a witness with respect to the alleged prior use. The board held that the opposition division's failure to hear the witness and the absence in the decision under appeal of any reference to a reason why it had not been necessary to hear the witness amounted to a fundamental procedural violation of the right to be heard.
In T 474/04 (OJ 2006, 129), the board held that if assertions made in an unsworn witness declaration remained contested, as a rule a request from a party to hear the witness had to be granted before these assertions were made the basis of a decision against the contesting party.
In T 909/03 the board held that it was not necessary for a party to be given a copy of the minuted testimony before questioning a witness appearing for the other party. During the oral proceedings the party had been given sufficient opportunity to comment on the testimony of the witness, even though the written minutes of the hearing were not available to the parties. No substantial procedural violation had thus occurred.
In T 716/06, the board confirmed that where oral evidence of a witness was requested by a party the competent department of the EPO should grant this request only if it considered this oral evidence necessary, i.e. when it was required to clarify matters that are decisive for the decision to be taken. However, where an opponent requested that a witness be heard on an alleged public prior use and on the disclosure of a certain feature by this prior use, the competent department of the EPO as a rule had to grant this request before deciding that the alleged public prior use was neither established nor constituted a novelty-destroying state of the art because it did not disclose the feature in question. In the case at issue, the opponent's right to be heard was violated. For more on hearing witnesses on alleged prior use, see also T 1100/07.