Abstract: A method for monitoring an error performance of each call in a digital exchange circuit has a plurality of subscriber terminals. The overall transmission system includes a plurality of circuits forming transit paths connecting the exchange circuit with each of the subscriber terminals. The method includes the steps of collecting and storing error check information of each transit path together with collected time of the information, and collecting and storing call information of each call. The call information includes call identification with terminal numbers of an originating subscriber terminal and a terminating terminal, transmission rate, start time and end time of a call, and the circuits through which the call is routed. A circuit accommodation database information is provided, which indicates which of the plurality of circuits form a path for each call.