A sample vessel (80) made of material with magnetic susceptibility .chi..sub.2, for containing a sample substance (87) with magnetic susceptibility .chi..sub.3.noteq..chi..sub.2 to be analyzed in a nuclear magnetic resonance (NMR) spectrometer, has an inner interface G.sub.2 toward the sample substance and an outer interface G.sub.1 toward the environment (85) that exhibits magnetic susceptibility .chi..sub.1. The shape of the interface toward the sample substance and the interface toward the environment are coordinated to match the discontinuities in susceptibility at the interfaces in such a way that on introduction of the sample tube filled with sample substance into the previously homogeneous magnetic field of an NMR spectrometer, the magnetic field inside the sample substance remains largely homogeneous.