Suspensions consisting of polymer-shelled microspheres are finding increasing use in a diverse range of technologies or applications, e.g. in the medical field, such as diagnostic imaging, drug and gene delivery and tissue engineering. In this work, a solution of water-insoluble polymethylsilsesquioxane was perfused through the outer needle of a co-axial needle arrangement while air was passed simultaneously through the inner needle, with both needles placed in an electric field. The liquid and air flow rates were varied but at 5 mu l s(-1) for each material stable microbubble formation was achieved at 5.7 kV. The microbubbles were collected in a vial of distilled water and they rapidly converted into polymer-shelled microspheres containing similar to 60 wt% liquid. Microscopic examination of the spheres within 300 s of preparation showed a large population of near-spherical polymer-shelled microspheres with a mean size of 6 +/- 2 mu m diameter near the water surface. After 48 h, the microspheres had collected at the bottom of the vial. The fact that the microspheres absorbed and encapsulated the liquid in which they were collected and the fact that their size (< 10 mu m) is suitable for vascular administration make this a new one-step preparation technology for microspheres used in biomedical applications.