Recombinant strains of Alcaligenes eutrophus harboring the polyhydroxyalkanoate (PHA) synthase gene of Aeromonas caviae synthesized poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyheptanoate) terpolymers from alkanoic acids of odd carbon numbers. The results indicated the specificity of PHA synthase of A. caviae toward 3-hydroxyalkanoate units from C-4 to C-7. The composition of the polyesters formed varied as the carbon numbers of the alkanoic acids fed increased.