In order to assess the sensitivity of nuclear magnetic resonance (NMR) in detecting acute renal vascular insufficiency, in vitro NMR spectroscopy (at 0.25 T) was performed on rabbit renal cortices following 45 min of unilateral renal artery (RAO) or renal vein occlusion (RVO). Data were obtained both with and without paramagnetic enhancement with gadolinium-DTPA (Gd-DTPA). In the absence of contrast material, RVO was distinguished by markedly elevated spin-lattice (T1) and spin-spin (T2) relaxation times when compared to the contralateral control kidney [mean increase of 29% in T1 (p less than 0.001) and 19% in T2 (p less than .001)]. RAO produced no change in T1 (p = N.S.) and a small change in T2 (mean increase of 11%, p less than .01). Five min following injection of 0.05 mM/kg of Gd-DTPA, relaxation times of control kidneys were markedly shortened [mean decrease 75% in T1 (p less than .001) and 12% in T2 (p less than 0.01)]. With Gd-DTPA, kidneys with RVO continued to have elevated T1 and T2 relaxation time, and kidneys with RAO maintained their essentially normal pre-contrast relaxation time values. We conclude that non-contrast NMR tissue analysis clearly differentiated normal from congested (RVO) kidneys, but not from acutely ischemic (RAO) kidneys. Paramagnetic enhancement with Gd-DTPA allows the differentiation of normally perfused from acutely ischemic or congested kidneys.