  The purpose of this paper is to obtain an integral representation for the
difference $f(L_1)-f(L_2)$ of functions of maximal dissipative operators. This
representation in terms of double operator integrals will allow us to establish
Lipschitz type estimates for functions of maximal dissipative operators. We
also consider a similar problem for quasicommutators, i.e., operators of the
form $f(L_1)R-Rf(L_2)$.
