Paolo Butta', Emanuele Caglioti, Carlo Marchioro On the violation of Ohm's law for bounded interactions (384K, PostScript file) ABSTRACT. We study the motion of a charged particle in a constant electric field interacting via Newton's law with an infinitely extended system of particles. We discuss conditions on the particle/medium interaction which are necessary for the charged particle to reach a finite limit velocity. For small electric field intensity, the linear response theory states that the drift velocity should be directly proportional to the field (Ohm's law). In the framework of fully Hamiltonian systems, we support the thesis that Ohm's law validity needs the interaction particle/medium to be unbounded. We prove this statement in a one-dimensional model, by showing that for bounded interactions the velocity of the charged particle increases linearly in time.