This graduation project focuses on transducers based on GMR phenomenon (abbreviation for giant magnetorresistance), set in gradiometric configuration and applied to the detection of metallic objects, magnetic or not, inserted in the human body. The envisioned technique, besides being non-invasive, reduces the risk of surgical failure and postoperative complications - significant advantages over traditional techniques. This document gathers a brief description of physical and mathematical modelling of the problem; explains the operation of GMR transducers and associated electronics and apparatus and, finally, reports the performance of the prototype tested over samples of different natures. This is, actually, the continuation of a research involving GMR sensores. These researches are conducted by the Laboratory of Biometrology, which is linked to the Posgraduation Programme in Metrology of PUC-Rio.