An imaging contrast medium comprising a physiologically tolerable multinuclear complex (as defined in claim 1) is disclosed. The multinuclear complex contains at least two, but preferably three or more contrast enhancing atoms. For X-ray or ultrasound imaging techniques heavy metal atoms are used to enhance contrast, whereas in Magnetic Resonance Imaging paramagnetic metal atoms are contrast enhancing. Molybdenum and tungsten are preferred contrast enhancing atoms. The medium may also be used therapeutically.