The EPO must be informed of the time when, and the place where, the enquiry is to take place and must inform the parties, witnesses and experts concerned.[Rule 150(5); ]

If so requested by the EPO, the competent authority shall permit the attendance of members of the department concerned and allow them to question any person giving evidence either directly or through the competent authority. Whether the parties may put questions or not will depend on the laws of the contracting states concerned.[Rule 120(3); Rule 150(6); ]