This Letter reports the temperature dependencies of the relaxation time T, (in the ranges: 100-440 K at 60 MHz; 20 K-RT at 24.667 MHz) and the second moment of the NMR line for protons (in the range: 100-350 K, 27 MHz) measured for a polycrystalline sample of 4-chloro-2-furfurylamino-5-sulfamoyl-benzoic acid (furosemide), form I. The minima in the temperature dependence of the T-1 time revealed two activation processes related to the proton transfer in the O-(HO)-O-... hydrogen bond (the low-temperature minimum) and a jumps of the -NH2 group (the high-temperature minimum). The reduction in the second moment value M-2 indicated a global motion of the compound molecule, a quasi-isotropic tumbling motion. (c) 2006 Elsevier B.V. All rights reserved.