World-wide a concern exists about the influence of man-made noise on marine life and particularly on marine mammals and fish. One of the acoustic polluters of the world’s oceans is high-power active sonar, but also pile driving and seismic activities at sea are of concern with respect to animal welfare. At TNO, acoustic criteria are being developed to protect marine animals from severe disturbance (or worse) due to man-made noise. One of the ‘stages’ in ‘dose-response relationships’ is the ‘discomfort threshold’, the received noise level at which a marine animal turns when approaching a noise source. In The Netherlands discomfort thresholds for a number of sound types have been determined for harbour porpoises, harbour seals and some North Sea fish species. This paper shows how those measurements were carried out and compares some results with proposed TNO dose-response relationships for marine mammals.