Acremonium chrysogenum was cultivated in a 30 1 stirred tank reactor on complex medium consisting of dry glucose syrup, corn steep liquor, amino acids, urea and inorganic salts, which was supplemented by soy oil in fed batch operation. The concentrations of biomass, the key medium components, the product and its precursors were monitored during cultivation. In addition the concentrations of intracellular amino acids and precursors and the enzyme activities of the biosynthesis were determined during cultivation. ACV formation is the bottleneck of the biosynthesis in good agreement with other authors. By amino acid supplements of the diluted complex medium very high concentration, productivity and yield coefficient of cephalosporin C were obtained. The Carbon balance indicates that at the end of the cultivation the fraction of P-lactam compounds increased to 55%. Only 15% of the carbon compounds could not be identified. (C) 2002 Elsevier Science Ltd. All rights reserved.