Recently we introduced the Reduced Surface as an efficient tool to built molecular surfaces. We describe here how this geometric construct can be used to efficiently reconstruct the solvent excluded surface of a protein for which the coordinates of a subset of atoms are changing. We show that, the complexity of that operation is not dependent upon the size of the molecule and is in O[tlog(t)] where t is the maximum of the number of probes and atoms involved in the reconstruction of the surface. The algorithms described here have been implemented and tested on several proteins. The triangulation of the solvent excluded surface of proteins in which a side chain was changing conformation could be updated at rates ranging from 7 to 22 frames per second. We also applied this method to compute the surface area fluctuation of the FIV protease undergoing a constrained molecular dynamics simulation (16 mobile residues). Rate of 6 frames per second were obtained in this case.