A possible integral representation of double commutators allowing non-vanishing mass of intermediate states is obtained. As expected, it reduces to Dyson's result on putting the masses to be zero. A discussion is also given showing how dispersive relatsions for non-forward scattering can be obtained on assuming the fourier transform F(q0, q) of the usual N|[j(x/2),j(-x/2)]|pN> to vanish not only for certain real q but also for asmall interval of imaginary q. It is pointed out that similar assumption is actually involved in customary proofs of dispersive relations.