The objective of this work was to evaluate the effect of particle size on steam-explosion pretreatment of herbaceous lignocellulosic biomass. Hemicellulose and cellulose recovery, and effectiveness of enzymic hydrolysis of the cellulosic residue is presented for steam-explosion pretreatment of an agriculture residue (Brassica carinata) using different particle sizes. The parameters tested were: particle size (2-5, 5-8 and 8-12 mm), temperature (190 and 210 degreesC), and residence time (4 and 8 min). The compositional analysis of filtrate and water insoluble fibre after pretreatment and enzymic digestibility data are presented. Larger steam-exploded particle (8-12 min) results in higher cellulose and enzymic digestibilities. The use of very small particles in steam explosion would not be desirable in optimising the effectiveness of the process improving economy. (C) 2002 Elsevier Science Ltd. All rights reserved.