We examined an effective administration method for an anti-cancer drug, and then a combination therapy of anti-cancer drug and hyperthermia (thermochemotherapy) was investigated. In the cases of insufficient heating such as 38.5 degrees C and 41.0 degrees C, administration of cis-diamminedichloroplatinum (CDDP) improved the cell killing effect. As the results of in vitro experiments, the cell killing effect in the thermochemotherapy increased to 90.2% at 38.5 degrees C and 98.0% at 41.0 degrees C from 72.5% and 89.0% with hyperthermia alone, respectively. This thermochemotherapy was applied to the tumor-formation experiment in vivo. In the case of hyperthermia alone, a palpable tumor was formed at 13 days after the injection of cells into a rat leg. However, in the case of the thermochemotherapy, no tumor tissue was observed over 3 months. It seems that the surviving cells from hyperthermia alone are killed by CDDP.