The positively charged fluorescent dye Rhodamine 123 (Rho 123) accumulates in mitochondria. An adriamycin (ADR)-resistant cell line derived from Ehrlich ascites tumor cells (wild EATC) was established in our laboratory. Overall mitochondrial activity of wild EATC and ADR-resistant EATC was investigated by the staining method with Rho 123. The uptake of Rho 123 into living cells was analyzed by flow cytometry. The intracellular Rho 123 uptake of ADR-resistant EATC was lower than that of wild EATC. The intracellular Rho 123 uptake of wild EATC increased when cells were treated with cepharanthine (CP). The intracellular Rho 123 uptake of ADR-resistant EATC increased markedly by CP treatment. ADR-resistant EATC cosumed more endogenous oxygen than wild EATC. The energy level of ADR-resistant EATC was discussed.