The main purpose of this work is the development of a reproducible experimental technique for supplying new data from cellulose pyrolysis at high heating rates and low residence times. The actual behavior of solid materials under such conditions (fast pyrolysis) is quite difficult to investigate experimentally. Data were collected in an entrained-flow reactor, accurately optimized to operate at low solids/gas ratios. Cellulose powder, mostly Avicell PH102, was conveyed by an inert carrier gas into a catalytically inert quartz tube with different heating sections. Weight loss and composition measurements were collected at temperatures between 400 and 650 degreesC, residence time between 50 and 140 ms, and nominal heating rates ranging from 6000 to 11000 K/s. The disturbance. effect of aggregative flow was demonstrated and quantified; all of the meaningful data were collected under conditions approaching the single-particle (homogeneous flow), while trying to keep the increasing experimental error bounded. The role of water loss during the initial heating of the particles is specifically addressed, together with its contribution to aggregation and further reactions. It is demonstrated that dilute particle suspensions lose water very rapidly. The particle size effect has been quantified as well, confirming that 90-mum particles are small enough to prevent any intraparticle processes.