A recombinant strain of Escherichia coli was used to produce poly(4-hydroxybutyric acid), P(4HB), homopolyester by fed-batch culture in M9 mineral salts medium containing glucose and 4-hydroxybutyric acid as carbon sources. The final cell dry weight, P(4HB) concentration and P( I HB) content were 12.6 g/l, 4.4 g/l, and 36% of cell dry weight, respectively, in a 27-1 stirred and aerated fermenter after 60 h of fed-batch fermentation at constant pH.