Cell-size unilamellar vesicles were made by removing solvents from microscopic chloroform spherules containing smaller water droplets within. The average diameter of the vesicles in a typical preparation was 9.2 mum, comparable to that of human erythrocytes (7 mum). The standard deviation of the size distribution was 3.0 mum. The unilamellarity and bilayer unit membrane of vesicles were demonstrated by transmission electron microscopy. Materials so far successfully incorporated into vesicles include glucose, sucrose, Arsenazo III and Ponceau S dyes, thymidine triphosphate, methotrexate, agarose, collagen, ferritin, polyadenylic aid, DNA, and whole bacteria. The captured volume per milligram of lipids (up to 144 microliter/mg) was almost an order of magnitude greater than the highest value reported in the literature to date (up to 15.6 microliter/mg) (Szoka, F.C. and Papahadjopoulos, D. (1978) Proc. Natl. Acad, Sci. U.S.A. 75, 4194-4198).