The synthesis of a new zwitterionic diblock copolymer poly(l-glutamic acid)-b-poly(l-lysine) (PGA-b-PLys) is described, and its self-assembly into schizophrenic vesicles that can reversibly be produced in moderate acidic or basic aqueous solutions is reported. These pH-sensitive nanoparticles are expected to be very promising candidates in macromolecular nanobiotechnologies.