Two kinds of large vesicles (average diameter: ca. 0.2 mu m) bearing complementary DNA strands aggregated to form densely packed clusters. Addition of Triton X-100 (1.2 mM) as a fusogenic reagent to an aqueous suspension of the vesicle-clusters induced successive fusion of vesicles, leading to a giant multilamellar vesicle-like sphere with a diameter of ca. 3 mu m.