An approach is developed to study the dynamics of protein conformational transitions in depth. A computational (Monte Carlo) approach based on a united residue model is used. Unbiased transitions between the Apo and Holo conformations/states of calmodulin are observed at the rate of 1 per day per processor. A series of models of increasing complexity is studied, accounting for hydrophobic interactions and calcium binding. Details of the transitional region and structural information about intermediate states are obtained. Statistically converged ensembles of transitions are obtained in a reasonable real time period.