  We reconsider the large $N$ asymptotics of Harish-Chandra-Itzykson-Zuber
integrals. We provide, using Dyson's Brownian motion and the method of
instantons, an alternative, transparent derivation of the Matytsin formalism
for the unitary case. Our method is easily generalized to the orthogonal and
symplectic ensembles. We obtain an explicit solution of Matytsin's equations in
the case of Wigner matrices, as well as a general expansion method in the
dilute limit, when the spectrum of eigenvalues spreads over very wide regions.
