Abstract: A method of detecting loopbacks on trunks in digital networks, comprises the steps of detecting an out-of-service trunk, continually placing a predetermined bit pattern on an outgoing channel of a trunk card, continually monitoring a receive channel of the trunk card to detect said bit pattern, and identifying the presence of a loopback when said bit pattern is persistently detected on the receive channel. This method avoids the need to dedicate a trunk channel for signaling purposes. By detecting the presence of loopbacks, intelligent networks can be prevented from unjustifiably clearing an alarm condition and returning traffic to a fault path.