The acquisition of resistance to anticancer drugs is an important problem in cancer chemotherapy. Ehrlich ascites tumor cells (wild type EAT cells) were grown in a medium containing 1 mu g/ml adriamycin (ADR) (ADR-resistant strain) and the cells that proliferated were established in our laboratory. Intracellular ADR accumulation and the killing effect of ADR in the ADR-resistant strain were markedly reduced compared with those of the wild type EAT cells. In this study, we initially observed thermosensitivity in both strains and found no difference in the thermosensitivity. These findings demonstrated that hyperthermic treatment was effective in the ADR-resistant strain as well as in the wild type EAT cells. On the other hand, thermotolerance is an important problem in the hyperthermic treatment of cancer. We next observed the thermotolerance of both strains and found that the thermotolerance in the ADR-resistant strain was greater than that in the wild type EAT cells, but the thermotolerance was almost restored within 24 hours. Furthermore, we investigated the influence of thermotolerance on the intracellular accumulation and killing effects of ADR in the wild type EAT cells. There was no difference in the intracellular ADR accumulation and the killing effect of ADR between non-thermoresistant cells and thermoresistant cells. These results suggested that hyperthermia was effective in the ADR-resistant cells either alone or combination with ADR.