An attempt to produce ethanol from a cellulosic substrate by a single-stage process using intergeneric hybrids obtained from Trichoderma reesei QM 9414 and Saccharomyces cerevisiae NCIM 3288 fusants is described. Two hundred one fused strains were isolated using two different combinations of hybridization, followed by polyethylene glycol treatment of protoplasts derived from parent and mutant strains. Some fusants were either diploids or heterokaryons, as verified by a protoplast fused system obtained by auxotrophic mutants derived from T. reesei QM 9414 and S. cerevisiae NCIM 3288. Of the 201 fusants, 170 were found to be relatively stable. Two fusants (M14 and M62) showed the highest synthesis of ethanol from filter paper cellulose, producing 0.0149 and 0.0191 g l-1, respectively. © 1994.