Cisplatin is a key chemotherapeutic agent for the treatment of esophageal cancer. We examined the intracellular localization of cisplatin in esophageal cancer cell lines and determined their sensitivity to cisplatin using in-air micro-PIXE (particle induced X-ray emission). Two human esophageal squamous cell carcinoma (ESCC) cell lines, TE-2 and TE-13, were examined for their response to cisplatin using MTT assay, flow cytometry, and DNA fragmentation assays. Real-time reverse transcription-polymerase chain reaction was also used to evaluate the mRNA expression of multidrug resistance protein 2 (MRP2) in both cell lines. Platinum localizations of intracellular and intranuclear were measured using in-air micro-PIXE. TE-2 cells were more sensitive to cisplatin than TE-13 cells (IC(50): 37.5 mum and 56.3 mum, respectively). Flow cytometry analysis confirmed that more TE-2 than TE-13 cells were in the sub-G1 phase. DNA fragmentation assay was analyzed to confirm the MTT assay and flow cytometry results. The expression of MRP2 mRNA in TE-13 cells was stronger than in TE-2 cells. In-air micro-PIXE showed that TE-2 cells had higher intracellular cisplatin concentrations than TE-13 cells and the ratio of intranuclear to intracellular cisplatin in individual cells was not significantly different. We observed the intracellular and intranuclear localization of cisplatin using in-air micro-PIXE. The results of this study suggest that in-air micro-PIXE could be a useful quantitative method for evaluating the cisplatin sensitivity of individual cells. Finally, we speculate that MRP2 in the cell membrane may play an important role in regulating the cisplatin sensitivity of ESCC cells.