As nuclear magnetic resonance imaging techniques have developed, a need for agents which can enhance and improve the natural tissue relaxation time differences has become apparent. Especially valuable would be agents that differentially alter NMR images in a manner related to tissue physiology and disease processes. Sophisticated para-magnetic and free radical contrast agents will be discussed in other papers in this issue. However, in this report, some common agents which are currently used in research and in human clinical studies for other purposes, but which can alter NMR contrast will be discussed. These agents include olive oil, estrogen hormones, diuretics, ethanol, glycerin, and dimethyl sulfoxide. Measurements of their relative effects on T1 and T2 of normal and cancerous breast tissues, a variety of body organs, and brain are presented. Some of these agents may have immediate practical applications in human NMR imaging studies.