P-31 relaxation in P-donor ligands bound to rhenium depends, at low fields, on (1)J(Re-P), and therefore is sensitive to the stereochemistry of the other ligands. The comparison of T-1’s can be used as a probe of the coordination geometry of the P-ligands in the case of isomers or when the ligands are bound differently to the same metal or (in polynuclear compounds) bound to different metals, provided that these have the same coordination sphere.