The Bloch group of a field,which is constructed using the five-term functional equation of the dilogarithm,arises in a variety of contexts: invaraiants of hyperbolic 3-manifolds,algebraic K-theory and the homology of GL2.We introduce a `refined version of the Bloch group.This is a module over the multiplicative group of the field whose coinvariants give the classical Bloch group.We will show how the re ned Bloch group allows us to calculate hitherto unknown parts of H3 of SL2 of local and global fields.