The National Renewable Energy Laboratory (NREL) has built and operated a pilot-plant to convert lignocellulosic feedstocks to ethanol for the U.S. Department of Energy (DOE). The process development unit (PDU) has a designed throughput of I ton (dry basis)/day of biomass and is equipped to handle a variety of feedstocks. Major processing systems include feedstock milling, pretreatment, simultaneous saccharification and fermentation (SSF), and ethanol distillation. Several experimental runs have been successfully completed since the startup of the plant in March 1995. The plant capabilities are continually being improved to meet the needs of our industrial partners and to facilitate NREL's process development work. This paper reports on various aspects of commissioning and operations, the present capabilities, and plans for use of the facility. Copyright (C) 1997 Elsevier Science Ltd.