The manner in which copolymer poly(HB-co-HV) production was influenced by different methods of limiting cell proliferation during the production phase was examined. Polymer production was significantly improved in fermentation strategies in which some growth was maintained, either by linear or exponential nitrogen source feeding as compared to cultures in which nitrogen supply was totally interrupted. Improved volumetric productivities were obtained in cultures fed with NH4OH and the proportion of 3HV incorporated was approximately twofold higher in these cultures. These performance improvements were due to higher specific rates of glucose and propionate consumption in cultures in which true growth capacity was maintained.