  We present a physically inspired generalization of equilibrium response
formulae, the fluctuation-dissipation theorem, to Markov jump processes
possibly describing interacting particle systems out-of-equilibrium. Here, the
time-dependent perturbation adding a potential V with small amplitude h(t)
changes the rates W(x,y) for the transition x --> y into W_t(x,y) = W(x,y) exp
{h(t)[bV(y)-aV(x)]} as first considered by Diezemann; a,b are constants. We
observe that the linear response relation shows a reciprocity symmetry in the
nonequilibrium stationary regime and we interpret the connection with dynamical
fluctuation theory.
