In SDI test using tetrazolium salt, we compared MTT with XTT, which has been recently developed and is more sensitive than MTT. Further, a chemosensitivity test with endoscopic biopsy specimens using XTT was conducted. The reproducibility of the MTT assay was assessed under various conditions. The I.I of MTT assay did not vary according to type or concentration of anticancer drugs and the biopsy site of specimens. Then MTT and XTT assay were compared, revealing the results of these 2 assays were significantly correlated. Thus, XTT assay was performed with tissues from surgical specimens using biotome. Of the 16 specimens subjected to XTT assay, 6 showed an OD value of 0.100 or more, which was well within assessment. XTT assay was also performed in biopsy specimens from patients using a biotome manipulated under endoscopic guidance before operation. Three among 6 specimens showed an OD value of 0.100 or more. Our findings have demonstrated that the SDI test using XTT can be used for the chemosensitivity test, even when these specimens contain a relatively small number of cells collected using a biotome.