We argue that the major driving force in protein folding is a gainin the water entropy. The formation of intramolecular hydrogen. bonds is important just for reducing the dehydration penalty as much as possible during the folding process. Focusing the physical basis on these two factors, we construct a new energy function which is calculated quite rapidly using our morphometric approach. Seven different proteins are chosen, and the native fold and over 600 misfolded structures are considered for each protein. It is shown that the energy function is always the lowest for the native structure. (c) 2007 Elsevier B.V. All rights reserved.