Increased interstitial fluid pressure (IFP) in solid tumors forms a barrier to transcapillary transport and thereby prevents response to chemotherapy. The current methods to determine IFP are invasive, are difficult to use in internal tumors,can measure pressure in only a few loci, and, therefore, cannot map the spatial distribution throughout the whole tumor.This study presents a noninvasive method to determine the spatial distribution of tumor IFP using slow infusion contras enhanced magnetic resonance imaging (MRI). MRI scanning is performed before and during a steady-state infusion of the contrast agent. Intra- and intertumoral variations in interstitial hypertension were demonstrated in xenografts of human lung and breast cancer in mice. The cover features a high-resolution image of the steady-state contrast agent concentration in a lung tumor (top), and a parametric image of the estimated interstitial fluid pressure (bottom), derived from analysis of the top image. The inserted graphs show the corresponding distribution of concentration and IFP across the long axis of the tumor. Our results indicate that transfer of the common gadolinium-based MRI contrast agents can be pressure-driven in the presence of elevated IFP and can serve to noninvasively map IFP and predict the presence of barriers to drug delivery. For details, see the article Hassid et al. on page 4159 of this issue.