Micelles of pluronic P85 (poly(oxyethylene)-poly(oxypropylene) block copolymer) are used as microcontainers for in vitro delivery of fluorescein into Jurkat and MDCK cells. In order to target the fluorescein containing micelles into the cell, Staphylococcus aureus enterotoxin B (SEB) is covalently conjugated with a pluronic molecule and the conjugate is incorporated into the micelle content. The incorporation of SEB capable of receptor-mediated endocytosis results in a drastic enhancement of the efficiency of cell loading with the fluorescent dye. This effect is not observed under the conditions (4 degrees C) when endocytosis is abolished.