When Cellulomonas flavigena CDBB-531 was grown on glucose, xylose, glycerol, solka floc, sugarcane bagasse or xylan, xylanase activity was found only in the fermentation broth, while beta-xylosidase activity was always associated with the cells. Both enzymes were inducible, sugar-cane bagasse was the best inducer, solka flee and avicel were moderately good, while xylan was poor. A synergistic effect on xylanase and beta-xylosidase synthesis was observed when cellulose and hemicellulose were used together as carbon sources. When this strain was grown on glucose, cellobiose, arabinose or xylose, only low levels of both enzymes were detected. These results indicate that xylanase and beta-xylosidase were carbon-source-repressed by readily metabolizable substrates. The effect of glycerol on enzymes that were already induced was studied. The addition of glycerol caused a significant decrease in the levels of xylanases, while beta-xylosidase activity remained unchanged.