Stable unilamellar vesicles form spontaneously upon mixing aqueous suspensions of long-chain lecithins (fatty acid chain lengths 14 carbons or longer) with small amounts (20 mol %) of micellar synthetic short-chain lecithins (fatty acid chain lengths 6-8 carbons). These vesicles are potentially ideal for any experiment (i.e., membrane protein reconstitution, drug delivery, etc.) that requires an easily formed, nonleaky unilamellar structure.