  We review various aspects of integrable hierarchies appearing in N=2
supersymmetric gauge theories. In particular, we show that the blowup function
in Donaldson-Witten theory, up to a redefinition of the fast times, is a tau
function for a g-gap solution of the KdV hierarchy. In the case of
four-manifolds of simple type, instead, the blowup function becomes a tau
function corresponding to a multisoliton solution. We obtain a new expression
for the contact terms that links these results to the Whitham hierarchy
formulation of Seiberg-Witten theories.
