ProVectin is hydrated with the target protein in physiological buffer. During this lipid hydration step liposomes form, and some of the protein that is dissolved in the hydration medium becomes encapsulated in the liposomes; depending on the physical properties of the protein, some of the protein is captured by association with the liposomal membane. The ProVectin/protein liposomes are placed on cultured cells where they attach to negatively charged cell surfaces. Following cell surface attachment the liposomes fuse directly with the plasma membrane and deliver the captured protein into the cell, or alternatively, the liposomes are endocytosed and then fuse with the endosome, releasing the liposome captured protein into the cytoplasm. ProVectin™ is remarkably effective for delivering a number of different macromolecules into the cytoplasm of cells; it can deliver fluorescently labeled antibodies, high and low molecular weight dextrans, phycoerythrin-BSA (300,000 Mol.Wt.), caspase 3, caspase 8, granzyme B, and b-galactosidase into the cytoplasm of a variety of different adherent and suspension cells. The efficiency varies from 20-100% of the cells transduced and up to 50% of the input protein gets incorporated into the cells.