We describe a standard set of quantity names and symbols related to the estimation of kinetic parameters from dynamic contrast-enhanced T1-weighted magnetic resonance imaging data, using diffusable agents such as gadopentetate dimeglumine (Gd-DTPA). These include a) the volume transfer constant Ktrans (min−1); b) the volume of extravascular extracellular space (EES) per unit volume of tissue ve (0 < ve < 1); and c) the flux rate constant between EES and plasma kep (min−1). The rate constant is the ratio of the transfer constant to the EES (kep = Ktrans/ve). Under flow-limited conditions Ktrans equals the blood plasma flow per unit volume of tissue; under permeability-limited conditions Ktrans equals the permeability surface area product per unit volume of tissue. We relate these quantities to previously published work from our groups; our future publications will refer to these standardized terms, and we propose that these be adopted as international standards. J. Magn. Reson. Imaging 10:223–232, 1999. © 1999 Wiley-Liss, Inc.