The effect of a phosphate feeding strategy and the optimal rate of biomass production (r(x)) during the production phase of P(3HB-co-3HV) in a 6-1 fermentor were determined in cultures of Ralstonia eutropha with the goal of enhancing polymer productivity. Rates of biomass production (r(x)) between 0.00 and 0.20 gxr l(-1) h(-1) were monitored during the production phase. When a low rate of cell growth was maintained (r(x) of 0.02 gxr l(-1) h(-1)), polymer production improved, resulting in a final cell mass, P(3HB-co-3HV) mass, and P(3HB-co-3HV) content of 98.2 g, 62.0 g and 63.1 wt%, respectively, after 27.3 h. The maximum polymer productivity obtained during the production phase was 1.36 g l(-1) h(-1).