Superconducting quantum interference devices usually are manufactured in thin film technology. With a noise level about 10(-15) Tesla/square-root Hertz, these devices represent the most sensitive magnetic field sensors. For measurements of the weak biomagnetic field of the human body additional measures are necessary in order to suppress external perturbations. The benefit of SQUID measurement technique for medical research and diagnostics originates in Amperes law, which describes the magnetic field as an universal action of the current field. Using the Biot-Savart formula and physical-physiological models, magnetic field data are used to reconstruct the current field in the human body.