This work describes the utilization of CO2 at sub- and supercritical conditions with 1-butanol/water as co-solvent in the delignification of sugar cane bagasse. The experiments were carried out using a factorial design procedure for four factors in two levels, using the following parameters and levels: temperature (150 and 190 degrees C), pressure (7 and 23 MPa), 1-butanol content (60 and 90%, v/v) and reaction time (45 and 105 min). The efficiency of the process was monitored by determining pulp yields, delignification extent, residual lignin and polyoses contents. The higher delignification extent (94.5%) was obtained at 7 MPa, 190 degrees C, 105 min and 60% 1-butanol in the co-solvent mixture. The results also indicate a low selectivity of the process once the lignin removal was accomplished by an extensive hydrolysis of the polysaccharide fraction. The best compromise between lignin removal and polysaccharide preservation was obtained at high pressures and low content of 1-butanol in the co-solvent mixture. (c) 2004 Elsevier B.V. All rights reserved.