The potential benefits of reducing the size of biomass into very fine particles in various pretreatment processes were investigated.  Two major points were addressed in this investigation.  The first was to verify whether the fine particle size improves the enzymatic digestibility under alkaline pretreatment conditions.  The second was to test the feasibility of high temperature-short treatment time neutral treatment of biomass.  The conditions explored are in the range of 190-220^oC and 5–60 seconds.  The extremely small particle size allows quick heating and uniform temperature within the biomass making high temperature-short treatment time feasible.  This approach was taken to see if such condition can alter the crystalline structure of the cellulosic component without decomposing the carbohydrates, and if so, how it affects the enzymatic digestibility.  Our data taken from switch grass and corn stover to this point indicate that size reduction to very fine particles gives significant improvement in pretreatment.  In the alkaline pretreatment, the improvement was due to increased surface area.  The benefit of high temperature treatment appears to be related with the alteration of the crystalline structure of cellulose.  The digestibility data of treated biomass affected are presented under various alkaline and neutral treatment conditions.  The data were further analyzed to verify the isolated effects of size reduction on biomass structure and pretreatment.