Gabrielli D., Jona-Lasinio G., Landim C., Vares M.-E. Microscopic Reversibility and Thermodynamic Fluctuations (22K, ApsTeX) ABSTRACT. In this paper we show that certain properties of thermodynamic fluctuations which were derived long ago by Onsager and Onsager-Machlup as a consequence of microscopic reversibility , can actually hold also if the dynamics deviates from reversibility. This result is based on the explicit construction of models which can be analysed rigorously. What happens is that small scale irreversibilities are washed out at the macroscopic level.