The dynamic properties of 111 backbone HN sites in uncomplexed human profilin, a protein of 139 residues, have been characterized by two-dimensional inverse-detected 1H- 15N NMR spectroscopy. Heteronuclear { 1H}- 15N nuclear Overhauser effects and 15N longitudinal and transverse relaxation rates have been analyzed in terms of model-free spectral density functions and exchange contributions to transverse relaxation rates. Relatively high mobilities on the nanosecond timescale are observed for Asp 26 and Ser 27, which form part of a loop connecting β-strands A and B, and for Thr 92 through Ala 95, which are in a loop connecting β-strands E and F. Significant exchange contributions, indicative of motions on the microsecond to millisecond timescale, have been obtained for 30 residues. These include Leu 77, Asp 80 and Gly 81 of a loop between β-strands D and E, Ser 84 and Met 85 of β-strand E, Gly 121 of a loop connecting β-strand G and the C-terminal helix, and Gln 138, which is next to the C-terminal residue Tyr 139. Some of the regions showing high flexibility in profilin are known to be involved in poly-L-proline binding.