Until now, most preparative methods used to form polymeric vesicles involve either organic cosolvents or sonication. In this communication, we demonstrate for the first time a detergent-aided method to produce polymersomes. Peptidic polymersomes were formed from the rod-rod block copolymer PBLG(36)-E, where PBLG is hydrophobic poly(gamma-benzyl l-glutamate) and E is a hydrophilic designed peptide. The block copolymer was first solubilized by detergent micelles in aqueous buffer, after which the concentration of detergent was reduced by dilution, transforming the particle morphology in solution from mixed micelles to polymersomes. The polymersome formation was monitored with dynamic light scattering and confirmed with transmission electron microscopy. Polymersomes with average diameters of approximately 300 nm were obtained as well as discs with average diameters of approximately 100 nm. This detergent-based method can be used to create polymersomes with a range of properties, as verified by its application to another biocompatible block copolymer, the flexible polybutadiene(46)-b-poly(ethylene glycol)(30). The technique will be particularly useful when delicate biomacromolecules such as (membrane) proteins, peptides, or nucleic acids are to be encapsulated in the polymersomes because the detergents used are compatible with these compounds, and the possible denaturing effect of sonication or organic solvents on the biological activity of the molecule of interest is avoided.