As part of an international effort to investigate a potential link between acoustic trials (SWAC 4) of SACLANTCEN with a stranding of Cuvier's beaked whales on the Greek coast in May 1996. TNO-FEL's Transient Detection Demonstrator (TDD). a tool to automatically search for submarine transients in passive sonar data, was adapted to the detection of Cetacean sounds. Notwithstanding the limited frequency interval available, sperm whales, small and medium sized toothed whales were detected and classifìed in the active sonar data recorded during the trials. For some sperm whales the distance and depth could be obtained using eigen ray tracing techniques. It was shown that the TDD can be used as a basis for the development of a real-time tool to search for the presence of Cetacean sounds prior to and during sonar transmissions.