Production of the glycopeptide antibiotic vancomycin by Amycolatopsis orientalis ATCC 19795 was examined in phosphate-limited chemostat cultures with biomass-recycle, employing an oscillating membrane separator, at a constant dilution rate (D = 0.14 h(-1)). Experiments made under low agitation conditions (600 rpm) showed that the biomass concentration could be increased 3.9-fold with vancomycin production kinetics very similar to that of chemostat culture without biomass-recycle. The specific production rate (q(vancomycin)) was maximal when the biomass-recycle ratio (R) was 0.13 (D = 0.087 h(-1)). When the dissolved oxygen tension dropped below 20% (air saturation), the biomass and vancomycin concentrations decreased and an unidentified red metabolite was released into the culture medium. Using increased agitation (850 rpm), used to maintain the dissolved oxygen tension above 20% air saturation, maximum increases in biomass concentration (7.9-fold) and vancomcyin production 1.6-fold (0.6 mg/g dry weight/h) were obtained when R was 0.44(D = 0.056 h(-1)) compared to chemostat culture without biomass-recycle. Moreover, at this latter recycle ratio the volumetric vancomycin production rate was 14.7 mg/L/h (a 7-fold increase compared to chemostat culture without biomass-recycle). These observations encourage further research on biomass-recycling as a means of optimising the production of antibiotics.