The EPFL and the VUB have been investigating the response of metal detectors within the framework of humanitarian demining research activities, in particular frequency domain systems. A simple circuit model has bene looked at first, followed by the analysis of a more completed model. As has also been stressed before, this analysis indicates the possibility of identifying some metallic objects. In addition the phase shift of the received signal turns out to be a continuous, monotonically decreasing function of the object size; this leads to the idea of imposing a 'phase threshold' in order to reduce the amount of detected clutter. This discrimination-based approach is less ambitious than object identification, but is likely to be more robust and to work when looking for metallic objects of a certain size, e.g. non minimum-metal mines or UXO. A first series of measurements was therefore carried out using a commercially available, differential tow frequent metal detector, the Foerster MINEX 2FD. The detector's internal signals have been recorded in a laboratory setup along linear scans varying different object parameters for several representative objects. The collection of data as a function of movement enables the possibility of analyzing the data in the complex plane, and makes it possible to exploit global object properties. Some representative results are presented and the limits of such discrimination/identification approaches briefly outlined.