Antitumor activity of the thermosensitive liposome, TAC-1043, was examined. The TAC-1043, produced by Takeda Chemical Industries, Ltd., contained entrapped cisplatin in a large unilamellar vesicle (LUV). LUV is composed of dipalmitoylphosphatidyl choline (DPPC) and distearoylphosphatidyl choline (DSPC) in the ratio of 9:1. The in vitro sensitivity of TAC-1043 was examined by SDI assay with MTT, using human esophageal cancer cell lines (TE-2, KY). TAC-1043 was effective at the concentration of 10 micrograms/ml, 41 degrees C and 43 degrees C. The in vivo effect of TAC-1043 together with hyperthermia was examined using mouse tumor MM 48. TAC-1043 combined with hyperthermia significantly suppressed the tumor proliferation.