This paper provides quantitative information on oxygen transfer as well as the kinetic and metabolic parameters related to oxygen uptake in Streptomyces coelicolor A3(2) cultured in a 20 dm(3) computer controlled bioreactor using both defined and complex media. It is evident from the literature that production of antibiotics is strongly affected by the dissolved oxygen concentration. Many processes of antibiotic fermentations have been developed to the point at which the microbial oxygen demand exceeds the oxygen transfer capability of the existing fermentation facilities. As a consequence, the oxygen transfer rate has become the rate limiting factor in such processes. It is necessary to know the oxygen kinetic and metabolic parameters of an aerobic fermentation for a successful scale-up and operational control of the process. In the literature, information concerning the oxygen uptake kinetics of the Streptomyces cultures is scarce despite their industrial importance. This paper, therefore, provides useful quantitative information on oxygen transfer and uptake rates in S. coelicolor cultures. In the defined medium, the total oxygen uptake rates were in the range of 5-6 mmol O-2 dm(-3) h(-1) throughout the active growth phase, the maximum specific oxygen uptake rate was 7.44 mmol O-2 g cell(-1) h(-1), the specific oxygen maintenance demand was 1.88 mmol O-2 g cell(-1) h(-1), and the k(L)a values were in the range of 40-100 h(-1). In the complex medium, however, the k(L)a values varied in the range of 18-70 h(-1).