Extension of Onsager's Reciprocity to Large Fields and the Chaotic Hypothesis

We show that the ``fluctuation theorem,'' a consequence of the chaotic hypothesis of G. Gallavotti and E. G. D. Cohen [Phys. Rev. Lett. 74, 2694--2697 (1995); J. Stat. Phys. 80, 931--970 (1995)] can be interpreted as extending to arbitrary forcing fields Green-Kubo's formulas, hence Onsager's reciprocity, in a class of reversible nonequilibrium statistical mechanical systems.