The influence of carbon and nitrogen sources on the production of exo-glucanase was investigated. The enzyme production was variable according to the carbon or nitrogen source used. Levels of b-cellobiohydrolase (CBH) were minimal in the presence of even low concentrations of glucose. Enzyme production was stimulated by other carbohydrates and thus is subject to carbon source control by easily metabolizable sugars. In Dubos medium, on cellobiose, the cellobiohydrolase titres were 2-to 110-fold higher with cells growing on monomeric sugars and 2.7 times higher than cells growing on other disaccharides. a-Cellulose was the most effective inducer of b-cellobiohydrlase and filter paperase (FPase) activities, followed by kallar grass straw. Exogenously supplied glucose inhibited the synthesis of the enzyme in cultures of Cellulomonas flavigena. Nitrates were the best nitrogen sources and supported greater cell mass, cellobiohydrolase and FPase production. During growth on a-cellulose containing 8-fold sodium nitrate concentration, maximum volumetric productivities (Q_p) of b-cellobiohydrolase and FPase were 87.5 and 79.5 IU/l./h respectively and are significantly higher than the values reported for some other potent fungi and bacteria.