Malignant tumors are characterized by abnormalities of the vasculature and interstitium, which may impede the distribution of drugs and imaging agents. Here we describe a method for estimating tumor interstitial permeability and elasticity based on fitting a spatio-temporal fluid dynamic model to the time course of interstitial pressure (IFP) measurements. The model assumes that sudden insertion of the IFP measurement needle transiently perturbs the steady-state fluid balance, which recovers over time as a function of the vascular and interstitial hydraulic conductivities (L p S and K), the interstitial bulk modulus (E) and the extracellular, extravascular volume fraction (φ). Initial simulations showed that the time course of IFP recordings was mainly determined by K and E/φ. Mean values of K and E/φ in 60 newly diagnosed cervix cancers were 1.5×10 −7 (SE 2.2×10 −8 ) cm 2 /mm Hg s and 2230 (SE 212) mm Hg, respectively. For comparison, K and E/φ were also measured in orthotopic ME-180 human cervix cancer xenografts and KHT-C fibrosarcomas in mice. K was higher in both of these tumors (7.0×10 −7 and 9.3×10 −7 ) than in cervix cancer, and E/φ was lower (497 and 433). To our knowledge, these are the first measurements of interstitial permeability and elasticity in individual human cancers. Serial evaluation of these parameters may provide a means of clinically monitoring response to treatments that specifically target the tumor microenvironment.