Abstract: The present invention provides methods for the production of poly-.beta.-hydroxyalkanoate copolymer comprising the steps of (a) introducing into a prokaryotic host cell a vector construct which directs the expression of a sequence which encodes a poly-.beta.-hydroxybutyrate biosynthetic pathway, (b) introducing into the host cell a vector construct which directs the expression of one or more proteins which regulate acetate and propionate metabolism, (c) culturing the host cell in medium containing propionate or a derivative thereof, and (d) isolating poly-.beta.-hydroxyalkanoate copolymer from the cultured host cell.