A Streptomyces fed-batch fermentation was studied with on-line measurement of dissolved carbon dioxide (DCO2). A selected cell strain R060107 of Streptomyces hygroscopicus was used in the production of rapamycin. pH was controlled only in the production phase at the low limit of 5.1 after its value dropped from an initial 6.5 to 5.1. DCO2 was used to control the feed in the fed-batch fermentation of S. hygroscopicus R060107. The experiment investigated the relationship between rapamycin production and the evolution of DCO2. A high limit of DCO2 (hDCO(2)) was used to control medium feed. In order to meet the needs for the dynamic growth and metabolism of cells in the process, the hDCO(2) was defined as a dynamic parameter, and was therefore calculated constantly in the process. A fermentation condition of limited nutrient supply was realized. It was observed that rapamycin was secreted when the glycerol concentration was well controlled in the fermentation condition. Experimental results showed that 500 mg/l of rapamycin was produced in 120 h of fermentation. (C) 2008 Elsevier Ltd. All rights reserved.