Improving the sensitivity of magnetic resonance imaging (MRI), a powerful non-invasive medical imaging technique, requires the development of novel contrast agents with a higher efficiency than gadolinium chelates such as DTPA-Gd (DTPA: diethylenetriaminepentaacetic acid) that are currently used for clinical diagnosis. To achieve this objective, the strategy that we have explored involves the use of gold nanoparticles as carriers for gadolinium chelates. These nanoparticles are obtained by reducing a gold salt in the presence of a dithiolated derivative of DTPA. Characterization of these particles by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), colorimetric titration, and X-ray photoelectron spectroscopy (XPS) reveals the presence of a multilayered shell containing about 150 ligands on 2-2.5 nm sized particles. These particles exhibit a high relaxivity (r(1) = 585 mM(-1) s(-1) as compared to 3.0 mM(-1) s(-1) for DTPA:Gd), rendering them very attractive as contrast agents for MRI.