Narrow-dispersity thermoresponsive block copolymers of poly(ethylene oxide)-block-poly(N-isopropylacrylamide) self-assemble into vesicles at temperatures above 32 degrees C. The vesicles integrate a hydrophobic fluorescent dye into their membranes and encapsulate the hydrophilic anticancer drug doxorubicin. Temperature-controlled release of the dye through disintegration of the vesicles takes place at temperatures below 32 degrees C, as shown in the figure.