In this paper, we al,ply for the first time two-dimensional (2D) correlation spectroscopy to analyze pressure-induced changes in proteins. We show that it is possible to distinguish between hydrogen-deuterium (H/D) exchange and conformational changes from the synchronous and the asynchronous spectra. From the sequence of the spectral changes it can be concluded that the initial partial unfolding of the secondary structure enhances the exchange, which is followed by further conformational changes. The exchange process is complete below ca. 0.4 GPa. The elastic distortions of the protein at higher pressures seem not to be accompanied by H/D exchange. (C) 1999 Elsevier Science B.V. All rights reserved.