Copolymers of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) were produced in a continuous culture of Alcaligenes eutrophus with 17.5 gl(-1) of fructose and 2.5 gl(-1) of pentanoic acid in the feed. The P(3HB-co-3HV) productivity was maximal at a dilution rate of 0.17h(-1) and yielded 0.31 gl(-1)h(-1) under an ammonium-limited condition. The 3HV content in copolymers increased from Il to 79 mol% as the dilution rate of cells was increased from 0.06 to 0.32h(-1).