AbstractThe ability ofL‐sorbose to stimulate cellulase production In shake flask culture ofTrichoderma reeseiwas examined in mineral salts media (initial pH 5.0) containing either 1.0%D‐xylose, 1.0% cellulose, and/or 0.1, 0.3, or 0.5%L‐sorbose. When sorbose was the only carbon source, growth was limited, little substrate was utilized, pH increased, and cellulase activity was not apparent. The other carbon sources promoted good growth, pH dropped sharply to 2.5–3.0, substrate was utilized rapidly, and cellulase activity was detected. After three weeks of fermentation, twice as much cellulase activity was detected in the medium containing only cellulose as the carbon source, as compared to xylose as the carbon source. Cellulase activity was higher when media contained xylose supplemented with sorbose compared to xylose as the only carbon source. At 0.3 and 0.5% levels of sorbose supplementation of xylose‐based media, cellulase activity was similar to that in cellulose‐