In the case of flexible molecules, the standard approach of transforming NOE intensities into spatial restraints and of building conformational models minimizing these restraints greatly neglects the richness of molecular conformations. Making use of NOE intensities measured in triplicate and of an iterative molecular-dynamics scheme, we optimized a force field to generate a set of conformations whose ensemble is compatible with the experimental data, and is weighted according to the Boltzmann distribution. This scheme is applied to two cyclic peptidomimetic ligands of integrins. Their difference in binding affinity is recapitulated in terms of their difference in conformational fluctuations.