Streptomyces ambofaciens was grown on a synthetic medium with glycerol (10g litre(-1)) and ammonium (20 mM) as carbon and nitrogen sources, respectively. Batch fermentation produced a specific production rare of spiramycin (q(sp)) of 0.3 mg h(-1) g(-1) DCW. Improvement of spiramycin production was achieved by fedbatch culture. The strong influence of the initial uptake rates of glycerol (q(gly)) and ammonium (q(NH4+)) on the specific production rate of spiramycin (q(sp)) was demonstrated by conducting several fermentations with continuous feeding of glycerol and ammonium, in different ratios. The specific production rate of spiramycin was increased 10 fold. A low specific growth rate was also necessary for spiramycin biosynthesis.