Theoretical work has suggested the existence of solvation/desolvation barriers in protein folding/unfolding processes. We propose that the energetic and structural consequences of such barriers for the folding transition state can be assessed from experimental unfolding rates using well-established structure-energetics relationships. For a set of proteins of size within the 60-130 number-of-residues range, we find energetic effects associated to solvation/desolvation on the order of 10(2) kJ/mol. This supports that the folding transition states may be characterized by large networks of water-unsatisfied, broken internal contacts. In terms of buried surface, we estimate the typical network size to be on the order of several thousands of A2, or approximately 50% of the total change in accessible surface area upon unfolding. The analyses reported here thus suggest a clear structural picture for the different energetic balance of native and folding transition states.