A method and apparatus for preparing a binary liquid, highly toxic cancer treatment pharmaceutical for administration to a patient from an I.V. bag is disclosed. Liquid components of the pharmaceutical are furnished in septum-sealed vials which are mixed in a syringe structure formed by a body having a mixing chamber in fluid communication with first and second ports. The vials are attached to the body at the first port, their septum is pierced, and a normally closed valve between the first port and the chamber is opened so that the liquid components flow along a sealed path into the chamber to prevent contact between the components and the surrounding environment. The I.V. bag is attached to the body at the second port and is pierced by a needle in response to movement of the bag towards the syringe body. This movement is used to open a valve between the second port and the chamber so that the mixed pharmaceutical can be flowed along a sealed path into the I.V. bag to prevent contact between the pharmaceutical and the environment until the transfer of the pharmaceutical to the bag has been completed. The syringe structure is inexpensive, can be injection molded, and is discarded after its use.