Combined biosynthesis and product separation has been successfully performed for the first time using a zonal centrifugal bioreactor-separator. The biosynthesis of dextran polymer from sucrose using the dextransucrase enzyme was investigated in order to evaluate bioreactor performance. The bioreactor consisted of a bowl, fitted with a Reorienting gradient rotor which facilitated substrate and enzyme loading and the reproducible unloading of solutions from the system. This allowed the distribution of substrate, enzyme and product materials in the bowl at the end of each trial to be accurately determined. Studies have indicated that combined bioreaction-separation is possible using this system. However, viscosity build-up in the bioreactor must be minimised in order to increase the yield of polymer product per unit time and improve product separation.