The sugar consumption rates and the product formation of yeasts (Saccharomyces cidri NCYC 775, S. cerevisiae NCYC 1047, S. cerevisiae ATCC 4132) and bacteria (Lactobacillus brevis DSM 20054, Lactococcus lactis ssp. lactis ATCC 19435, Escherichia coli ATCC 11303, Zymomonas mobilis ATCC 31821) were investigated in spent sulphite liquor and an enzymatic hydrolysate of steam-pretreated Salix caprea at different pH values in order to elucidate the suitability of the organisms with respect to future genetic engineering approaches. The possible inhibitory action of the two substrates on the investigated microorganisms was also considered S. cerevisiae emerged as one of the better candidates, owing to its fast sugar consumption rate and efficient ethanol production.