Three genes from Ralstonia eutropha necessary for poly(3-hydroxybutyrate) (PHB) synthesis were introduced into the hairy roots of sugar beet, Transformation of a vector construct harbouring the PHB genes, each fused to the coding region of the pea ribulose-bisphosphate carboxylase plastid targeting sequence, resulted in 20 transgenic hairy-root clones, producing up to 55 mg high molecular PHB/g dry weight, as identified by gas chromatography, gel permeation chromatography and HPLC. Accumulation of PHB polymer in sugar beet root leucoplasts was confirmed by transmission electron microscopy. Thus, for the first time. plastidic PHB production was demonstrated for roots of a carbohydrate-storing crop plant.