A pulsed field gradient NMR (= nuclear magnetic resonance) method using stimulated echoes for determining the translational isotropic or anisotropic diffusion coefficient of a molecule or supramolecular assembly or the flow rate and direction of fluids containing such molecules is characterized in that the molecule or supramolecular assembly contains one or several isotopes (X) of non-zero nuclear spin other than protons having longitudinal relaxation times T1(X) that are longer than the longitudinal relaxation times T1(H) of the protons, and that the information about the localisation of the molecule or supramolecular assembly during the diffusion or flow interval is temporarily stored in the form of longitudinal magnetisation of said isotope or isotopes. Thus, the determination of translational diffusion coefficients or flow rates of supramolecular assemblies or molecules with short T1(H) values, in particular of supramolecular assemblies or molecules with M ≥ 50 kDa is accomplished.