It is a striking feature of the bacterial storage polymer poly-3-hydroxybutyrate (PHB) that, although the isolated polymer is highly crystalline, native PHB storage granules in cells are only found in an amorphous, mobile state. It has recently been proposed that the failure of PHB granules to crystallize is simply the result of slow nucleation kinetics that are operative for small particles. In support of this new model, we report here a straightforward procedure by which pure crystalline PHB can be reconstituted into submicron-size artificial granules. In the artificial granules, a synthetic surfactant has been substituted for the native granule coating. The artificial granules are amorphous and stable in suspension, and they are essentially indistinguishable from their native counterparts in terms of size, morphology, molecular mobility, and density. Furthermore, when the surfactant coating is removed from the artificial granules by dialysis, the granules crystallize, verifying the nucleation hypothesis. In vivo, the PHB granule surface is likely to consist of both protein and phospholipid; in vitro it is possible to prepare amorphous PHB granules which are stabilized solely by phospholipid. PHB artificial granule latexes crystallize well on drying and annealing, making them potentially useful in the preparation of polymer coatings; Artificial amorphous granules may also be prepared from other bacterial polyhydroxyalkanoates (PHAs) and from blends of incompatible polyesters.