A liposome for use in encapsulating both hydrophobic and hydrophilic substances (i.e., a "payload"),is disclosed which is capable of delivering their load upon the occurrence of a trigger or control condition. The liposomes are formed to stably encapsulate a particular active agent to form a delivery vehicle for the agent. The liposomes of the delivery vehicle are stable in a particular environment but become unstable or permeable if passed from the stable environment (e.g., characteristic of a particular pH and/or temperature and/or ionic strength) to a changed or unstable environment, thereby delivering their payload.