We have developed a new device that allows precise guided surgery through gamma-camera images in real time. It consists of a portable mini gamma camera combined with an image guided surgery system. We call this new instrument the "Gamma Functional Navigator." The small gamma camera has been built by our group and has a spatial resolution of about 2 mm. The position and orientation of the gamma camera and the surgical instruments is determined by the navigator through infrared reflectors. A software program combines the images obtained by the gamma camera at two different positions to form a stereoscopic image of the object under study. We have focused our interest, as a starting point, to the simplest problem of quasi-punctual objects, such as lymph nodes or small tumors. We have tested the "Gamma Functional Navigator" with different phantoms finding the position of the node in 3-D space with a resolution better than 3 mm for node-camera head distances lower than 5 cm. This allows to locate and distinguish cancerous nodes from its neighbors during surgery.