Spin-labelling has found wide applications in elucidation of the dynamic behaviour of biological macromolecules in aqueous media and biomembranes. Most of the proposed methods aimed at estimation of macromolecular correlation times (re) assume, however, spin label molecules rigidly bound within the protein matrix. To avoid this limitation theoreUcal models which involve additional dynamic parameters to characterize the spin label motion should be considered. We have used ESR spectra analysis technique which permits quantitative separatioa of slow macromolecular rotafion (described by the rotational correlation time, re) and fast anisotropic relative to protein nitroxyl radical motion (described by the "order parameter", S). This method was applied to study: i) conformational dynamics of covalently and non-covalently spin-labelled human serum albumin (HSA) in solution; ii) protein-protein (antigen-antibody) interactions in a model system containing spin-labelled bovine serum albumin (BSA) and anti-BSA immunoglobulin (IgG) in solution; and iii) dynamic properties of membrane-bound proteins: H+-ATPase (CF1-CF 0 coupling factor of photophosphorylation) and Photosystem I pigrnent-protein reaction centre complex (PSI RC) isolated from spinach chloroplasts and reconstituted in proteoliposomes.