A method for plant monitoring with a fieldbus of process automation technology, wherein a plurality of field devices communicate with a process control unit and a plant monitoring unit The method steps are carried out as follows: the regular, process-control, data traffic on the fieldbus is monitored by the plant monitoring unit; an examination of the telegrams of the regular data traffic for information indicating a diagnostic event at one of the field devices is performed; and in case a telegram is detected having an indication of a diagnostic event, the plant monitoring unit requests further diagnostic information from the pertinent field device.