Studies are reported of relaxation modifiers for use in nuclear magnetic resonance (NMR) imaging systems. Chelate complexes of transition metal salts are under investigation to determine their ability to reduce the spin-lattice relaxation time (T1) of the nucleus under observation and to reduce the toxicity of the metal ion. The ethylenediaminetetraacetate (EDTA) complexes of FeCl3, GdCl3, and MnCl2 are not as effective as the respective salts in reducing T1 of water protons at 90 MHz. For Mn, this diminution in ability is offset by a significant reduction in toxicity. Explanations for this loss of effectiveness are discussed.