Pretreatment water solubles were characterized to reveal the presence of inhibitory compounds to hydrolysis and fermentation. For reactions carried out at 180 C for 6 min, lower concentrations of xylose and arabinose were observed in these liquid fractions. Hence, these conditions were not strong enough to promote detectable modifications in the chemical composition of elephant grass, which remained almost unchanged after pretreatment (Table 2). The concentration of xylose and arabinose increased in the water solubles when higher severities were used for pretreatment (Table 3A). As a result, cellulosic substrates pretreated at high severities had lower concentrations of these carbohydrate components. Water washing of steam-exploded samples that were drained after pretreatment removed much lower concentrations of water soluble components (Table 3B). On the other hand, most of the elephant grass glucans remained in the solid fraction after pretreatment.